What is the difference between revenue and profit in the context of Edexcel International A Levels Economics?

In the context of Edexcel International A Levels Economics, revenue refers to the total income a business earns from selling its goods or services. It is calculated by multiplying the price per unit by the number of units sold. Profit, on the other hand, is the financial gain a business makes after deducting all its costs from the total revenue. Profit is an indicator of the business's financial health and efficiency.

How do fixed and variable costs affect a business's profit?

Fixed costs are expenses that do not change with the level of production, such as rent and salaries. Variable costs fluctuate with the level of output, like raw materials and direct labor. To calculate profit, a business must subtract both fixed and variable costs from its total revenue. Understanding the balance between these costs helps businesses in strategic planning and maximizing profits, a key concept in Edexcel International A Levels Economics.

Why is understanding break-even analysis important for businesses?

Break-even analysis is crucial for businesses as it helps determine the point at which total revenue equals total costs, resulting in neither profit nor loss. This analysis aids in decision-making regarding pricing, budgeting, and financial planning. For students studying Edexcel International A Levels Economics, mastering break-even analysis is essential for understanding how businesses plan for profitability and manage financial risks.

What role does marginal cost play in profit maximization?

Marginal cost is the additional cost incurred by producing one more unit of a product. In profit maximization, businesses aim to produce up to the point where marginal cost equals marginal revenue, as this is where profit is maximized. Understanding this concept is vital for Edexcel International A Levels Economics students, as it illustrates how businesses make production decisions to optimize profits.

How can businesses use profit margins to assess their performance?

Profit margins, which are calculated by dividing profit by revenue, provide insights into a business's efficiency and profitability. A higher profit margin indicates better financial health and cost management. For students of Edexcel International A Levels Economics, analyzing profit margins is a key skill in evaluating business performance and understanding competitive positioning in the market.

Why is "Treating normal profit as 'zero profit' or as a loss (thinking the firm makes no money)" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Students hear 'normal profit is where TR = TC' and assume the firm earns nothing. How to avoid it: Normal profit is a positive reward — the opportunity cost of enterprise — counted as a COST and included in AC. When AR = AC the firm earns NORMAL profit (fine, just no supernormal surplus). 'Zero ECONOMIC profit' and 'normal profit' are the same thing. Source: WEC13 Examiner Reports

Why is "Claiming supernormal profit when AR only equals AC (or drawing the profit rectangle when AR = AC)" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Students forget that normal profit is already inside AC, so a surplus needs AR strictly above AC. How to avoid it: Supernormal profit requires AR > AC. If AR = AC there is only NORMAL profit and no rectangle; if AR < AC it is a LOSS. Check the vertical gap between AR and AC at the profit-maximising output. Source: WEC13 mark schemes

Why is "Using ATC (average total cost) instead of AVC in the short-run shut-down rule" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Students apply the long-run 'cover all costs' idea to the short run without spotting that fixed costs are unavoidable there. How to avoid it: In the SHORT run compare AR with AVC (produce if AR ≥ AVC), because fixed costs are paid anyway; use AC/ATC only for the LONG-run decision (stay if AR ≥ AC). Source: WEC13 Examiner Reports — a recurring error

Why is "Getting the profit-maximising rule wrong (e.g. saying maximise TR, or produce where AR = AC)" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Revenue maximisation (MR = 0) and break-even (AR = AC) get confused with profit maximisation. How to avoid it: Profit is maximised where MC = MR. Revenue is maximised where MR = 0; AR = AC is the break-even (normal profit) point. These are three different outputs — keep them separate. Source: WEC13 Examiner Reports

Why is "Reading the price off the MR curve instead of the AR curve on the profit diagram" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Because MC = MR is used to find the output, students carelessly read the price at the same MR height. How to avoid it: Use MC = MR only to find the OUTPUT Q*. Then go straight UP from Q* to the AR (demand) curve to find the price P*. The price is always on AR, never on MR. Source: WEC13 Examiner Reports — recurring diagram error

Why is "Confusing profit with revenue (calling TR the profit)" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Both are money figures, so students stop at total revenue when a question asks for profit. How to avoid it: Profit = TR − TC — you MUST subtract total cost. A large revenue can still be a loss. In a profit question, always bring in both revenue and cost. Source: WEC13 Examiner Reports

Edexcel International A Levels Economics (XEC11-YEC11)

Profits and losses (Revenue, Costs and Profits)

Q: Why is "Using ATC (average total cost) instead of AVC in the short-run shut-down rule" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Students apply the long-run 'cover all costs' idea to the short run without spotting that fixed costs are unavoidable there. How to avoid it: In the SHORT run compare AR with AVC (produce if AR ≥ AVC), because fixed costs are paid anyway; use AC/ATC only for the LONG-run decision (stay if AR ≥ AC). Source: WEC13 Examiner Reports — a recurring error

Q: Why is "Getting the profit-maximising rule wrong (e.g. saying maximise TR, or produce where AR = AC)" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Revenue maximisation (MR = 0) and break-even (AR = AC) get confused with profit maximisation. How to avoid it: Profit is maximised where MC = MR. Revenue is maximised where MR = 0; AR = AC is the break-even (normal profit) point. These are three different outputs — keep them separate. Source: WEC13 Examiner Reports

Q: Why is "Reading the price off the MR curve instead of the AR curve on the profit diagram" a common mistake in Profits and losses (Revenue, Costs and Profits)?

Why it happens: Because MC = MR is used to find the output, students carelessly read the price at the same MR height. How to avoid it: Use MC = MR only to find the OUTPUT Q*. Then go straight UP from Q* to the AR (demand) curve to find the price P*. The price is always on AR, never on MR. Source: WEC13 Examiner Reports — recurring diagram error

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Short Notes - Profits and losses (Revenue, Costs and Profits)

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Detailed Study Notes

Detailed notes on Business Behavior for Edexcel International A Levels Economics, covering key concepts, explanations, examples, and exam-focused revision points.

Profits and Losses — Edexcel IAL Economics (WEC13) Study Notes

Profit is what is left when you put costs and revenue together: profit = total revenue − total cost. Learn the difference examiners reward every series — normal profit (a cost of production, earned when AR = AC) versus supernormal profit (AR > AC) versus a loss (AR < AC) — master the profit-maximising rule MC = MR and the short-run (AR ≥ AVC) and long-run (AR ≥ AC) shut-down conditions, and draw the supernormal-profit rectangle on a cost-revenue diagram. These are the exact AO2 diagram marks and AO3 analysis Unit 3 tests.

At a glance

Profit = total revenue − total cost ( $\text{Profit} = TR - TC$ ); equivalently, profit per unit is $(AR - AC)$ , so total profit $= (AR - AC) \times Q$ .
Normal profit is the minimum reward needed to keep the entrepreneur in the industry. It is a cost of production and is earned when AR = AC (equivalently TR = TC).
Supernormal (abnormal) profit is profit over and above normal profit — earned when AR > AC (TR > TC).
A loss (subnormal profit) occurs when AR < AC (TR < TC) — the firm is not even covering all its costs.
The profit-maximising rule is to produce where MC = MR (marginal cost equals marginal revenue).
Short-run shut-down: keep producing only if AR ≥ AVC — price at least covers average variable cost.
Long-run shut-down: stay in the market only if AR ≥ AC — price covers all costs.
Economic profit deducts all costs including opportunity cost (normal profit); accounting profit deducts only explicit money costs, so it is larger.
Role of profit: it signals where to move resources, gives an incentive to be efficient, rewards risk-taking, and funds investment.

What you’ll learn

Mapped to the Pearson Edexcel International A Levels XEC11-YEC11 syllabus (2020-2026).

3.2.4 — Define profit as total revenue minus total cost and calculate it from data.
3.2.4 — Distinguish normal profit (a cost of production, AR = AC), supernormal profit (AR > AC) and loss (AR < AC).
3.2.1 / 3.2.4 — Apply the profit-maximising rule that a firm produces where MC = MR.
3.2.4 — Explain the short-run shut-down condition (produce if AR ≥ AVC) and the long-run shut-down condition (produce if AR ≥ AC).
3.2.4 — Distinguish economic profit (deducts opportunity cost) from accounting profit (deducts explicit costs only).
3.2.4 — Evaluate the role of profit in a market economy (signals, incentives, rewarding risk, funding investment).

What profit is: total revenue minus total cost

Profit is what is left after costs. Profit = TR − TC, and profit per unit = AR − AC.

Profit is the reward a firm keeps after paying for everything it used. It is the single most important number in the theory of the firm because it ties together the two things you have already studied — revenue (money coming in) and costs (money going out).

The definition examiners want is simple:

$\text{Profit} = \text{Total revenue} - \text{Total cost} = TR - TC$

If a firm's total revenue is £2,000 and its total cost is £1,500, its profit is $2000 - 1500 = £500$ . If total cost were £2,300 instead, profit would be $2000 - 2300 = -£300$ — a loss.

There is a second, equally useful way to write profit that works per unit. Since $AR = TR \div Q$ (average revenue = price) and $AC = TC \div Q$ (average cost), the profit on each unit is the gap between them, and total profit is that gap times the number of units:

$\text{Profit} = (AR - AC) \times Q$

This per-unit version is the one you draw: on a cost-revenue diagram the vertical gap between AR and AC is the profit (or loss) per unit, and multiplying by the output Q gives a rectangle whose area is the total profit. Keep both forms ready — data questions usually want $TR - TC$ , while diagram questions want $(AR - AC) \times Q$ .

Crucially, profit is not the same as revenue. A firm can have a huge total revenue and still make a loss if its costs are higher. When a question asks about profit, you must bring in both revenue and cost — never answer a profit question with revenue alone.

Profit = total revenue − total cost (Profit = TR − TC).
Per unit: profit = (AR − AC) × Q — this is the version you draw as a rectangle.
AR is average revenue (= price); AC is average cost.
A big revenue can still be a loss if total cost is higher — profit ≠ revenue.
Data questions want TR − TC; diagram questions want (AR − AC) × Q.

See the full worked example for profits and losses (revenue, costs and profits) →

Normal profit, supernormal profit and loss

Normal profit (AR = AC) is a cost; supernormal profit is AR > AC; a loss is AR < AC.

Economists split "profit" into three cases, and the distinction between them is one of the most heavily rewarded ideas in Unit 3.

Normal profit is the minimum reward the entrepreneur must earn to keep supplying the good — just enough to stop them moving their resources to the next best alternative. Because it is the reward needed to keep the firm in the industry, economists treat normal profit as a cost of production (specifically the opportunity cost of enterprise), and it is included inside average cost (AC). A firm earns exactly normal profit when:

$AR = AC \quad (\text{equivalently } TR = TC)$

At this point the firm is "breaking even" in the economist's sense — covering all costs including the reward the owner could have earned elsewhere.

Supernormal profit (also called abnormal profit, or economic profit) is profit over and above normal profit. Because normal profit is already inside AC, any surplus of revenue over cost is supernormal profit. It arises when:

$AR > AC \quad (\text{equivalently } TR > TC)$

Loss (subnormal profit) is when the firm cannot even cover its costs, so it earns less than normal profit:

$AR < AC \quad (\text{equivalently } TR < TC)$

The single sentence to memorise: normal profit means AR = AC, supernormal profit means AR > AC, and a loss means AR < AC. Everything else in this subtopic hangs off that comparison of average revenue with average cost.

Normal profit = the minimum reward to keep the entrepreneur in the industry; it is a COST, inside AC.
Normal profit is earned when AR = AC (TR = TC) — 'breaking even' in the economist's sense.
Supernormal (abnormal / economic) profit is earned when AR > AC (TR > TC).
A loss (subnormal profit) occurs when AR < AC (TR < TC).
Everything comes down to comparing average revenue (AR) with average cost (AC).

The profit-maximising rule: produce where MC = MR

A profit-maximiser produces the output where marginal cost equals marginal revenue (MC = MR).

To maximise profit, a firm chooses its output using one rule:

$\text{Produce where } MC = MR$

The logic is marginal thinking. Marginal revenue (MR) is the extra revenue from one more unit; marginal cost (MC) is the extra cost of that unit.

If MR > MC, the extra unit adds more to revenue than to cost, so making it raises profit — the firm should expand.
If MR < MC, the extra unit adds more to cost than to revenue, so making it cuts profit — the firm should contract.
Profit stops rising and is at its maximum exactly where the two are equal: MC = MR.

At that output the firm cannot add to profit by producing either more or less, so it has squeezed out every available pound of profit.

Two cautions. First, MC = MR finds the profit-maximising output; the price is then read off the AR (demand) curve above that output — not off MR. Second, for the point to be a maximum (not a minimum), MC must be rising through MR. So the rule locates the output; the AR curve then gives the price; and comparing that price with AC tells you whether the firm makes supernormal profit, normal profit or a loss.

Do not confuse this with revenue maximisation. A revenue-maximiser produces where MR = 0 (the mid-point of AR); a profit-maximiser produces where MR = MC. Because MC is normally positive, the profit-maximising output is smaller than the revenue-maximising output.

Profit is maximised at the output where MC = MR.
MR > MC → expand (extra unit adds more to revenue than cost); MR < MC → contract.
MC = MR gives the OUTPUT; the price is read off the AR (demand) curve above that output, not off MR.
For a maximum, MC must be rising as it cuts MR.
Profit-max (MR = MC) ≠ revenue-max (MR = 0); profit-max output is smaller.

See the full worked example for profits and losses (revenue, costs and profits) →

Drawing supernormal profit on a cost-revenue diagram

Find Q* where MC = MR, read P* off AR and C* off AC, then shade the (P* − C*) × Q* rectangle.

Now put revenue and cost on one diagram and read off the profit. This is the AO2 diagram the exam rewards most in this subtopic, so learn to build it in a fixed order.

Build it in this order — the geometry examiners check:

Draw the four curves. A downward AR (demand) curve and, below it and twice as steep, the MR curve (this is a price-maker). A U-shaped MC and a U-shaped AC, with MC cutting AC at AC's minimum.
Fix the output first. Find Q* where MC = MR and drop a vertical line to the axis. This is the profit-maximising output.
Read the price off AR. Go straight up from Q* to the AR curve to find the price P* — the price is on AR, never on MR.
Read average cost off AC. At the same output Q*, the height of the AC curve gives the cost per unit C*.
Shade the rectangle. Because $AR > AC$ here, $P^{*} > C^{*}$ , so there is a positive gap. The supernormal profit is the rectangle between AR (top, at P*) and AC (bottom, at C*), from the axis across to Q*: its area is $(P^{*} - C^{*}) \times Q^{*}$ .

If instead $AC$ lay above AR at Q* (so $C^{*} > P^{*}$ ), the same rectangle would be a loss. If AR just touched AC at Q* (so $P^{*} = C^{*}$ ), the firm would make exactly normal profit and there would be no rectangle at all.

Draw AR (downward), MR (below AR, twice as steep), U-shaped MC and U-shaped AC (MC cuts AC at its minimum).
Fix Q* FIRST where MC = MR, then drop a line to the output axis.
Read the price P* by going up from Q* to the AR curve — never to MR.
Read cost per unit C* off AC at the same output Q*.
Supernormal profit = the rectangle between AR and AC up to Q*, area (P* − C*) × Q*.

See the full worked example for profits and losses (revenue, costs and profits) →

Shut-down conditions: short run (AR ≥ AVC) and long run (AR ≥ AC)

In the short run, keep producing if AR ≥ AVC; in the long run, only if AR ≥ AC.

A loss-making firm faces a choice: keep producing at a loss, or shut down. The right answer depends on the time frame, because in the short run the firm is stuck paying its fixed costs whatever it does.

Short-run shut-down condition — produce if AR ≥ AVC. In the short run, fixed costs (rent, leased machinery) must be paid even at zero output — they are unavoidable in the short run. So the firm should compare price (AR) with average variable cost (AVC), the costs it can avoid by stopping:

If AR ≥ AVC, the price covers all the variable cost and leaves something over to pay towards the fixed costs. Producing makes a smaller loss than shutting down, so the firm keeps going even though it is losing money overall.
If AR < AVC, the price does not even cover variable cost — every unit adds to the loss on top of the unavoidable fixed costs. The firm shuts down in the short run, losing only its fixed costs.

The break-even for staying open in the short run is therefore the shut-down point, where AR = AVC (the bottom of the AVC curve).

Long-run shut-down condition — produce only if AR ≥ AC. In the long run, all costs are variable — there are no unavoidable fixed costs, because the firm can end leases, sell machinery and exit entirely. So a firm will only stay in the market if the price covers all its costs:

If AR ≥ AC, the firm covers all costs (at least normal profit), so it stays.
If AR < AC, it is failing to cover full costs and could do better elsewhere, so in the long run it leaves the industry.

Summary: short run — keep going if AR ≥ AVC (cover variable costs and contribute to fixed); long run — stay only if AR ≥ AC (cover all costs). The difference is entirely about whether fixed costs are avoidable — they are not in the short run, but they are in the long run.

Short run: keep producing if AR ≥ AVC (price covers variable cost and contributes to unavoidable fixed costs).
If AR < AVC in the short run, shut down — every unit adds to the loss.
Short-run shut-down point is where AR = AVC (bottom of the AVC curve).
Long run: stay only if AR ≥ AC (all costs, including fixed, are now avoidable).
The whole difference is whether fixed costs are avoidable — no in the short run, yes in the long run.

Economic vs accounting profit, and the role of profit

Economic profit deducts opportunity cost too; profit signals, incentivises, rewards risk and funds investment.

Economic profit vs accounting profit. The two differ in which costs they subtract.

Accounting profit = total revenue − explicit (money) costs only, such as wages, materials, rent actually paid. This is the figure in a firm's published accounts.
Economic profit = total revenue − all costs, including implicit costs / opportunity cost (the reward the owner's money, time and capital could have earned elsewhere — i.e. normal profit).

Because economic profit subtracts more (the opportunity cost as well), it is smaller than accounting profit. A firm can show a healthy accounting profit yet make zero or negative economic profit if it is only just covering — or failing to cover — what its resources could earn elsewhere. When economists say "supernormal profit" they mean positive economic profit; "normal profit" means zero economic profit (all costs, including opportunity cost, exactly covered).

The role of profit. Profit is not just a reward — in a market economy it does several jobs:

Signalling: supernormal profit in an industry signals that it is worth entering; losses signal that resources should leave. Profit guides resources to where consumers value them most.
Incentive / efficiency: the chance of profit gives firms an incentive to cut costs, innovate and produce efficiently — those who do keep more profit.
Reward for risk: profit rewards the entrepreneur for taking the risk of committing resources with no guarantee of success.
Funding investment: retained profit is a major source of finance for investment in new capital, research and expansion, without borrowing.

These roles are exactly what you draw on in evaluation — for example, arguing that supernormal profit, though it looks like it harms consumers, can fund the investment and innovation that benefits them later.

Accounting profit deducts explicit (money) costs only; economic profit also deducts implicit / opportunity cost (normal profit).
Economic profit is SMALLER than accounting profit (it subtracts more).
Supernormal profit = positive economic profit; normal profit = zero economic profit.
Role of profit: signalling (guides resources), incentive/efficiency, reward for risk, and funding investment.
The 'role of profit' points are prime evaluation material in 14- and 20-mark questions.

Quick recap

Profit = total revenue − total cost (TR − TC); per unit, profit = (AR − AC) × Q.
Normal profit is a COST (the minimum reward to stay in the industry), earned when AR = AC (TR = TC).
Supernormal (abnormal / economic) profit is earned when AR > AC; a loss is AR < AC.
Profit is maximised where MC = MR; the price is then read off AR above that output.
On the diagram, supernormal profit is the rectangle between AR and AC up to Q*, area (P* − C*) × Q*.
Short-run shut-down: keep going if AR ≥ AVC; long-run shut-down: stay only if AR ≥ AC.
Economic profit deducts opportunity cost (normal profit) as well as money costs, so it is smaller than accounting profit.
Profit signals where resources should move, incentivises efficiency, rewards risk and funds investment.

Memorise this

Verbatim phrases and definitions Edexcel mark schemes credit.

Profit = total revenue − total cost (Profit = TR − TC); total profit = (AR − AC) × Q.
Normal profit is a cost of production — the minimum reward to keep the entrepreneur in the industry — earned when AR = AC (TR = TC).
Supernormal (abnormal) profit is earned when AR > AC; a loss (subnormal profit) when AR < AC.
A profit-maximising firm produces where MC = MR; the price is read off the AR curve above that output.
Short-run shut-down: produce only if AR ≥ AVC. Long-run shut-down: produce only if AR ≥ AC.
Economic profit deducts opportunity cost (normal profit) as well as money costs, so it is smaller than accounting profit.

How it’s examined

A central Unit 3 (WEC13) theory-of-the-firm topic, spec 3.2.1/3.2.4, and highly examinable. Tested in Section A (a 1-mark MCQ, e.g. identifying normal profit as AR = AC, or spotting the short-run shut-down condition AR ≥ AVC), and heavily in Section B, Q7: part (a) [2, Calculate] works out profit or supernormal profit from data (TR − TC, or (AR − AC) × Q); part (b) [4, Explain what is meant by] defines a term such as normal profit; part (c) [6, Analyse] requires a labelled cost-revenue diagram showing how a firm earns supernormal profit (the profit rectangle between AR and AC at Q* where MC = MR); part (d) [8, Examine] develops two analytical points (e.g. the short-run shut-down condition AR ≥ AVC); and part (e) [14, Discuss = KAA 8 + Eval 6] evaluates a profit-based claim. It also anchors Section C 20-mark Evaluate essays [KAA 12 + Eval 8], e.g. on whether a loss-making firm should always shut down. Examiner reports repeatedly flag: reading the price off MR instead of AR, drawing the profit rectangle up to the wrong output or with corners off the curves, confusing normal profit with zero profit, using ATC instead of AVC in the short-run shut-down rule, and treating profit as the same as revenue in calculations. Fully labelled cost-revenue diagrams with the profit rectangle drawn correctly secure the AO2 marks; correct formula → substitution → answer secures the calculation marks.

Sources: Pearson Edexcel International Advanced Level Economics (XEC11/YEC11) Specification, Issue 2; Edexcel IAL Economics WEC13 Examiner Reports; Edexcel IAL Economics WEC13 mark schemes. Last reviewed 2026-07-01.

Take this whole topic with you

Step-by-step worked examples — Profits and losses (Revenue, Costs and Profits)

Step-by-step solutions to past-paper-style questions on profits and losses (revenue, costs and profits), written exactly the way a tutor would explain them at the board.

Question type:

1Calculate profit from total revenue and total cost
Getting startedDirect calculation• WEC13 Section B(a) style• profit, calculation, AO2
Question
A firm sells 500 units at a price of £12 each. Its total cost is £4,800. Calculate the firm's profit. (2 marks)
Step-by-step solution
1. Step 1
  Find total revenue. $TR = P \times Q = £12 \times 500 = £6{,}000$ .
  $TR = P \times Q = 12 \times 500 = £6{,}000$
2. Step 2
  Apply the profit formula. $\text{Profit} = TR - TC = 6{,}000 - 4{,}800$ .
  $\text{Profit} = TR - TC$
3. Step 3
  Answer. $\text{Profit} = £6{,}000 - £4{,}800 = £1{,}200$ .
  $\text{Profit} = 6{,}000 - 4{,}800 = £1{,}200$
Answer
TR = £12 × 500 = £6,000; profit = £6,000 − £4,800 = £1,200.
Examiner tip
2/2 (AO2): 1 mark for TR = £6,000 (or the method TR = P × Q), 1 for profit = £1,200 using Profit = TR − TC. Show the £ unit. A common slip is stopping at TR (£6,000) and calling that the profit — profit is what is LEFT after cost.
2Calculate supernormal profit from AR and AC
Getting startedDirect calculation• WEC13 Section B(a) style• supernormal profit, calculation, AO2
Question
At its profit-maximising output a firm produces 200 units. Its average revenue is £15 and its average cost is £11. Calculate the supernormal profit. (2 marks)
Step-by-step solution
1. Step 1
  Profit per unit. Supernormal profit per unit is the gap between average revenue and average cost: $AR - AC = 15 - 11 = £4$ .
  $AR - AC = 15 - 11 = £4$
2. Step 2
  Scale up by output. Total supernormal profit $= (AR - AC) \times Q$ .
  $\text{Supernormal profit} = (AR - AC) \times Q$
3. Step 3
  Answer. $(15 - 11) \times 200 = £4 \times 200 = £800$ .
  $(15 - 11) \times 200 = £800$
Answer
Supernormal profit = (£15 − £11) × 200 = £4 × 200 = £800.
Examiner tip
2/2 (AO2): 1 mark for profit per unit £4 (AR − AC), 1 for £800 after multiplying by Q. Because AR > AC the profit is SUPERNORMAL. On a diagram this £800 is the area of the profit rectangle between AR and AC up to Q.
3Classify normal profit, supernormal profit or loss
Building confidenceIdentify & classify• WEC13 Section A / B style• normal profit, supernormal profit, loss, AO1
Question
For each firm, state whether it is making normal profit, supernormal profit or a loss, and justify it: (i) AR = £20, AC = £20; (ii) AR = £30, AC = £24; (iii) AR = £18, AC = £22. (4 marks)
Step-by-step solution
1. Step 1
  Recall the rule. Compare average revenue with average cost: normal profit when $AR = AC$ , supernormal profit when $AR > AC$ , a loss when $AR < AC$ .
2. Step 2
  (i) AR = AC (£20 = £20) → normal profit. The firm exactly covers all its costs, including the normal profit already inside AC.
3. Step 3
  (ii) AR > AC (£30 > £24) → supernormal profit of £6 per unit — revenue per unit exceeds cost per unit.
4. Step 4
  (iii) AR < AC (£18 < £22) → a loss of £4 per unit — the price does not cover average cost.
Answer
(i) normal profit (AR = AC); (ii) supernormal profit of £6/unit (AR > AC); (iii) a loss of £4/unit (AR < AC).
Examiner tip
The single decision is AR vs AC. Note (i) is NORMAL profit, not 'zero profit' or a loss — normal profit is a cost already inside AC, so AR = AC means the firm is doing fine.
4Find the profit-maximising output (MC = MR)
Building confidenceMulti-step problem• WEC13 Section B(c)/(d) style• profit maximisation, MC = MR, AO2
Question
A firm's marginal revenue and marginal cost at successive units are: Q = 1 (MR £18, MC £6); Q = 2 (MR £15, MC £9); Q = 3 (MR £12, MC £12); Q = 4 (MR £9, MC £16). State the profit-maximising output and explain your choice. (4 marks)
Step-by-step solution
1. Step 1
  Apply the rule. A profit-maximiser produces where $MC = MR$ .
  $\text{Produce where } MC = MR$
2. Step 2
  Scan the table. At Q = 1 and Q = 2, $MR > MC$ , so each extra unit adds more to revenue than to cost — keep expanding. At Q = 3, $MR = MC$ (£12 = £12).
3. Step 3
  Check the next unit. At Q = 4, $MR < MC$ (£9 < £16), so the 4th unit would reduce profit. The firm stops at Q = 3.
4. Step 4
  Conclude. Profit is maximised at Q = 3, where MC = MR (£12). Producing more or less would lower profit.
Answer
Profit-maximising output is Q = 3, where MC = MR (£12). Below it MR > MC (expand); above it MR < MC (contract).
Examiner tip
The mark is for MC = MR and the marginal logic (MR > MC → expand; MR < MC → contract). Remember MC = MR gives the OUTPUT; the price would then be read off the AR curve, not off MR.
5Draw a supernormal profit diagram
StretchGraph or diagram• WEC13 Section B(c) style• diagram, supernormal profit, MC = MR, AO2
Question
Using a cost-revenue diagram, show how a price-making firm earns supernormal profit. (6 marks)
Step-by-step solution
1. Step 1
  Set up the axes and curves. Put Cost, revenue (£) on the vertical axis and Output (Q) on the horizontal axis. Draw a downward AR (demand) curve with MR below it and twice as steep, plus U-shaped MC and AC (MC cutting AC at its minimum).
2. Step 2
  Fix the output first. Mark Q* where MC = MR and drop a vertical line to the axis — this is the profit-maximising output.
  $MC = MR \Rightarrow Q^{*}$
3. Step 3
  Read price and cost at Q*. Go up from Q* to AR to find the price P*, and read AC at the same output to find cost per unit C*. Because $AR > AC$ , $P^{*} > C^{*}$ .
4. Step 4
  Shade the rectangle. The supernormal profit is the rectangle between AR (top, P*) and AC (bottom, C*) up to Q*: area $= (P^{*} - C^{*}) \times Q^{*}$ .
  $\text{Supernormal profit} = (P^{*} - C^{*}) \times Q^{*}$
Answer
At Q* (where MC = MR) the price P* on AR lies above cost C* on AC, so the firm earns supernormal profit equal to the shaded rectangle (P* − C*) × Q*.
Examiner tip
Diagram marks (AO2): labelled axes, AR/MR/MC/AC, Q* at MC = MR, price read off AR (NOT MR), and the profit rectangle between AR and AC. The single most common error is reading the price off MR — it must come from the AR curve above Q*.
6Apply the short-run shut-down condition
StretchMulti-step problem• WEC13 Section B(d) style• shut-down, AVC, loss minimisation, AO2
Question
A firm's price is £9. At its current output, average variable cost is £7 and average total cost is £13. Should the firm keep producing in the short run? Justify with the shut-down condition. (6 marks)
Step-by-step solution
1. Step 1
  Note it is loss-making. $AR = £9 < AC = £13$ , so the firm makes a loss of £4 per unit. The question is whether to keep going or shut down.
2. Step 2
  Apply the short-run rule. In the short run, keep producing if AR ≥ AVC, because fixed costs must be paid even at zero output.
  $\text{Short run: produce if } AR \geq AVC$
3. Step 3
  Compare AR with AVC. $AR = £9 > AVC = £7$ , so the price covers all variable cost and leaves £2 per unit as a contribution towards fixed costs.
4. Step 4
  Conclude (loss-minimising). Producing gives a smaller loss than shutting down (which would still incur the full fixed costs), so the firm should keep producing in the short run — even though it is loss-making overall.
Answer
Yes — keep producing. AR (£9) ≥ AVC (£7), so the price covers variable cost and contributes £2/unit to fixed costs, giving a smaller loss than shutting down. In the long run, though, AR < AC (£9 < £13), so it would eventually leave.
Examiner tip
The rule uses AVC, not ATC — the £2 'contribution to fixed costs' is the key idea, so it is loss-MINIMISING to stay open. Note the contrast: in the long run AR < AC would trigger exit.

Model Answers — Profits and losses (Revenue, Costs and Profits)

High-scoring sample answers for profits and losses (revenue, costs and profits) on the Pearson Edexcel IAL XEC11 / YEC11 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
WEC13/01 Section B, Q7(a) style — Calculate (2 marks, AO2)2 marks
[Easy · 2 marks · Section B(a)] At its profit-maximising output a firm sells 300 units at an average revenue of £14. Its average cost is £9. Calculate the firm's supernormal profit.
Model answer
Supernormal profit is the gap between average revenue and average cost, multiplied by output:

$\text{Supernormal profit} = (AR - AC) \times Q = (14 - 9) \times 300$

$= £5 \times 300 = £1{,}500$

Profit per unit (1): $AR - AC = 14 - 9 = £5$ . Total (1): $£5 \times 300 = £1{,}500$ .
Why this scores
2/2: correct profit per unit £5 (AR − AC) (1) and correct total £1,500 after × Q (1). Because AR > AC the profit is SUPERNORMAL. Showing formula → substitution → answer secures both marks and guards against slips.
Question 2
WEC13/01 Section B, Q7(b) style — Explain what is meant by (4 marks, AO1)4 marks
[Easy · 4 marks · Section B(b)] Explain what is meant by normal profit.
Model answer
Normal profit is the minimum reward an entrepreneur must earn to keep supplying a good and to stop them moving their resources to the next best alternative use (1). Because it is the reward needed to keep the firm in the industry, economists treat it as a cost of production — the opportunity cost of enterprise — and include it within average cost (AC) (1).

A firm earns exactly normal profit when its average revenue equals its average cost, AR = AC (equivalently TR = TC) (1). At this point the firm is 'breaking even' in the economist's sense: it covers all its costs, including the reward the owner could have earned elsewhere, but makes no supernormal profit on top (1).
Why this scores
4/4: 'minimum reward to keep the entrepreneur in the industry' (1); 'a cost of production / opportunity cost of enterprise, included in AC' (1); 'earned when AR = AC / TR = TC' (1); development that this is break-even with no supernormal surplus (1). Calling normal profit 'zero profit' or 'no profit' is the classic error to avoid.
Question 3
WEC13/01 Section B, Q7(c) style — Analyse (6 marks), diagram expected, KAA Levels 1–36 marks
[Medium · 6 marks · Section B(c)] With the help of a diagram, analyse how a firm can earn supernormal profit.
Model answer
A firm earns supernormal profit when its average revenue exceeds its average cost (AR > AC) at the output it chooses to produce. To show this, draw a cost-revenue diagram with Cost, revenue (£) on the vertical axis and Output (Q) on the horizontal axis, with a downward-sloping AR (demand) curve, MR below it and twice as steep, and U-shaped MC and AC curves.

The firm first chooses its profit-maximising output, Q*, where MC = MR. This is the profit-maximising rule: while marginal revenue exceeds marginal cost, each extra unit adds more to revenue than to cost and so raises profit; the firm expands until MC = MR, where profit is greatest.

At that output the price is read off the AR (demand) curve — call it P* — while the average cost at the same output is read off the AC curve — call it C*. Because the firm has some market power (a downward-sloping AR), the price P* lies above the average cost C*.

The supernormal profit is therefore the rectangle between AR (top, at P*) and AC (bottom, at C*), stretching from the vertical axis across to Q*. Its area equals (P* − C*) × Q* — profit per unit multiplied by the number of units. Because normal profit is already included within AC, this surplus above AC is genuinely supernormal (abnormal) profit.
Why this scores
6/6 (Level 3): identifies the profit-maximising output at MC = MR, reads the price off AR (not MR) and average cost off AC at that output, and identifies the supernormal profit as the rectangle (P* − C*) × Q* between AR and AC — noting AR > AC and that normal profit is inside AC. Naming MC = MR and reading price off AR are the discriminators. Diagram marks (AO2) are awarded separately.
Question 4
WEC13/01 Section B, Q7(d) style — Examine (8 marks), KAA Levels 1–38 marks
[Medium · 8 marks · Section B(d)] Examine why a loss-making firm may continue to produce in the short run.
Model answer
A loss-making firm has $AR < AC$ , so it is not covering its total costs. Whether it should keep producing in the short run turns on the short-run shut-down condition: a firm continues to produce as long as average revenue covers average variable cost, AR ≥ AVC.

Point 1 — fixed costs are unavoidable in the short run. In the short run at least one factor is fixed, so fixed costs (e.g. rent, leased machinery) must be paid even at zero output. Shutting down does not escape them. This means the relevant comparison is not with total cost but with the costs the firm can actually avoid by stopping — its variable costs (AVC).

Point 2 — producing can minimise the loss. If AR ≥ AVC, the price covers all variable cost and leaves something over as a contribution towards the fixed costs. For example, if AR = £9 and AVC = £7, each unit contributes £2 towards fixed costs. Producing therefore results in a smaller loss than shutting down, where the firm would lose the whole of its fixed costs. So a loss-making firm keeps going to minimise its loss, not because it is profitable.

The limit. This only holds while AR ≥ AVC. If the price falls below AVC (AR < AVC), each unit produced adds to the loss on top of the fixed costs, so the firm should shut down in the short run, losing only its fixed costs. And in the long run, when all costs become avoidable, the firm will only stay if it covers all costs (AR ≥ AC); a persistent loss-maker will eventually exit. So continuing to produce at a loss is a purely short-run, loss-minimising decision.
Why this scores
8/8 = KAA Level 3 (7–8): two developed points — fixed costs are unavoidable in the short run, so the firm compares AR with AVC; and if AR ≥ AVC producing gives a 'contribution to fixed costs' and a smaller loss than shutting down — combined into the loss-minimising logic, with the AR < AVC limit and the long-run (AR ≥ AC) contrast. 'Examine' at Unit 3 is KAA-only (no evaluation marks). Using ATC instead of AVC caps the answer. Any diagram marks (AO2) are awarded separately.
Question 5
WEC13/01 Section B, Q7(e) style — Discuss (14 marks) = KAA (8) + Evaluation (6), diagram expected14 marks
[Hard · 14 marks · Section B(e)] Discuss the view that supernormal profit is always bad for consumers.
Model answer
Supernormal profit is profit over and above normal profit, earned when AR > AC at the firm's profit-maximising output (where MC = MR). On a cost-revenue diagram (Cost, revenue (£) vertical, Output (Q) horizontal) it is the rectangle between AR and AC up to Q*, area (P* − C*) × Q*.

The case that it harms consumers. A firm earning large supernormal profit typically has market power and a downward-sloping AR curve, meaning it can set a price above marginal cost. Consumers therefore pay a higher price and receive a smaller quantity than under perfect competition, transferring surplus from consumers to the firm — a loss of allocative efficiency. Persistent supernormal profit can also be a sign of weak competition (e.g. a monopoly protected by barriers to entry), which can lead to complacency, higher costs and less choice. On these grounds supernormal profit can look bad for consumers.

The case that it can benefit consumers. However, supernormal profit also plays important roles. First, it is a signal: high profits attract new firms into the industry, which increases supply, lowers prices and competes the supernormal profit away over time — so consumers benefit indirectly. Second, retained supernormal profit is a major source of funds for investment in new technology, capacity and research and development, which can lower costs and bring better or cheaper products in future (dynamic efficiency). Third, the prospect of profit gives firms a powerful incentive to innovate and cut costs, again benefiting consumers over the longer term.

Evaluation. Whether supernormal profit is 'always' bad depends on how it is used and on the market structure. If the profit is protected by high barriers to entry and simply extracted through high prices with no reinvestment, consumers lose. But if the market is contestable, so profit attracts entry and is competed away, or if the firm reinvests in innovation, consumers can end up better off. It also depends on the time frame: in the short run high prices harm consumers, but in the long run the signalling and investment roles can improve outcomes. Judgement: supernormal profit is not always bad for consumers — it harms them where market power is entrenched and profit is not reinvested, but it can benefit them where it signals entry, funds innovation or drives efficiency. The word 'always' makes the claim too strong.
Why this scores
KAA (8): explains supernormal profit (AR > AC at MC = MR, the profit rectangle) and develops the harm (price above MC, allocative inefficiency, weak competition) AND the benefits (signalling entry, funding investment/R&D, incentive to innovate). Evaluation (6): weighs barriers to entry / contestability, whether profit is reinvested, and short vs long run, reaching a 'not always — it depends' judgement rather than a flat verdict. The contestability and reinvestment criteria are the discriminators that lift Evaluation. Diagram marks (AO2) are awarded separately.
Question 6
WEC13/01 Section C style — Evaluate (20 marks), answer two of three, KAA 12 + Evaluation 820 marks
[Hard · 20 marks · Section C] Evaluate the view that a loss-making firm should always shut down.
Model answer
A firm makes a loss when its average revenue is below its average cost (AR < AC), so it is not covering its total costs. It is tempting to conclude that such a firm should always shut down, but the correct answer depends on the time frame and on the shut-down conditions, so the claim that it should always stop is too strong.

Why a loss-making firm might rightly keep producing (short run). In the short run at least one factor is fixed, so fixed costs must be paid even at zero output — shutting down does not avoid them. The relevant test is therefore the short-run shut-down condition: keep producing if price covers average variable cost, AR ≥ AVC. If AR ≥ AVC, the price covers all variable cost and leaves a contribution towards fixed costs, so producing gives a smaller loss than shutting down (which would lose the whole of the fixed costs). On a diagram, a firm producing where MC = MR with AVC ≤ AR < ATC is minimising its loss by staying open. There may also be strategic reasons to continue: keeping skilled staff and customers, maintaining supply contracts, and avoiding the cost of closing and later re-opening. The loss may also be temporary — caused by a recession or a short-term cost shock — so shutting down would sacrifice future recovery. In all these cases, not shutting down is the rational choice.

Why a loss-making firm should shut down. However, if AR < AVC, the price does not even cover variable cost, so every unit produced adds to the loss on top of the fixed costs. Here the firm should shut down in the short run, losing only its fixed costs. Moreover, in the long run all costs become variable and avoidable, so the firm should stay only if it covers all its costs (AR ≥ AC). A firm making a persistent loss — where AR is permanently below AC with no realistic prospect of recovery — should leave the industry and reallocate its resources to a more profitable use; that exit is exactly how markets move resources away from products consumers value less.

Evaluation and judgement. Whether a loss-making firm should shut down depends on the time frame and on how price compares with AVC and AC. In the short run it should keep producing if AR ≥ AVC (loss-minimising) but shut down if AR < AVC; in the long run it should exit only if it cannot cover full costs (AR < AC). It also depends on whether the loss is temporary or permanent, and on strategic factors such as retaining staff, contracts and market position. The most defensible conclusion is that a loss-making firm should not always shut down: it should shut down in the short run only when price fails to cover average variable cost, and exit in the long run only when it cannot cover average total cost. Otherwise, continuing to produce is the loss-minimising — and correct — decision. The claim is therefore true only in specific cases, not as a universal rule.
Why this scores
Top level on both strands. KAA (12): accurate short-run rule (produce if AR ≥ AVC because fixed costs are unavoidable — the 'contribution to fixed costs' loss-minimising logic) and long-run rule (exit if AR < AC), developed as multi-stage chains with reference to a cost-revenue diagram, plus strategic/temporary-loss reasons to continue. Evaluation (8): distinguishes short run from long run, AVC from AC, and temporary from permanent losses, reaching a context-dependent 'shut down only if AR < AVC (short run) or AR < AC (long run)' judgement rather than a flat verdict. The time-frame and AVC-vs-AC distinctions are the discriminators that push Evaluation to the top level. Any diagram marks (AO2) are awarded separately.

Key Formulae — Profits and losses (Revenue, Costs and Profits)

The formulae you need to memorise for profits and losses (revenue, costs and profits) on the Pearson Edexcel IAL XEC11 / YEC11 paper, with every variable defined in plain English and a note on when to use it.

Profit
$\text{Profit} = TR - TC$
$\text{Profit}$
profit (or loss if negative)
$TR$
total revenue = P × Q
$TC$
total cost
When to use
To calculate profit from total figures. Positive means a profit; negative means a loss. This is the definition of profit examiners expect.
Example
TR = £6,000, TC = £4,800 ⇒ profit = 6,000 − 4,800 = £1,200.
Profit from AR, AC and output
$\text{Profit} = (AR - AC) \times Q$
$AR$
average revenue (price per unit)
$AC$
average (total) cost per unit
$Q$
quantity of output
When to use
To find total profit from per-unit figures — and it is the version you DRAW: (AR − AC) is the height of the profit rectangle and Q is its width.
Example
AR = £15, AC = £11, Q = 200 ⇒ profit = (15 − 11) × 200 = £800 (supernormal).
Profit-maximising rule
$MC = MR$
$MC$
marginal cost (extra cost of one more unit)
$MR$
marginal revenue (extra revenue from one more unit)
When to use
To find the profit-maximising OUTPUT. Produce where MC = MR; then read the price off the AR curve above that output. If MR > MC expand; if MR < MC contract.
Example
MR = MC = £12 at Q = 3 ⇒ profit-maximising output is 3 units.
Short-run shut-down condition
$AR \geq AVC$
$AR$
average revenue (= price)
$AVC$
average variable cost
When to use
To decide whether a loss-making firm keeps producing in the SHORT run. If AR ≥ AVC the price covers variable cost and contributes to fixed costs, so producing minimises the loss; if AR < AVC, shut down.
Example
AR = £9, AVC = £7 ⇒ AR ≥ AVC, so keep producing (smaller loss than shutting down).
Long-run shut-down condition
$AR \geq AC$
$AR$
average revenue (= price)
$AC$
average (total) cost
When to use
To decide whether a firm stays in the market in the LONG run, when all costs are variable. Stay only if AR ≥ AC (price covers all costs, at least normal profit); otherwise exit.
Example
AR = £9, AC = £13 ⇒ AR < AC, so in the long run the firm leaves the industry.

Key Definitions and Keywords — Profits and losses (Revenue, Costs and Profits)

Definitions to memorise and the exact keywords mark schemes credit for profits and losses (revenue, costs and profits) answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IAL XEC11 / YEC11 sitting.

Profit
Examiner keyword
The surplus of total revenue over total cost: Profit = TR − TC. Positive means a profit; negative means a loss. It is what is left after all costs are paid.
Normal profit
Examiner keyword
The minimum reward needed to keep the entrepreneur supplying the good and to stop resources moving to their next best use. It is a cost of production (the opportunity cost of enterprise), included in average cost, and is earned when AR = AC (TR = TC).
Supernormal (abnormal) profit
Examiner keyword
Profit over and above normal profit — the surplus earned when AR > AC (TR > TC). It is the same as positive economic profit.
Loss (subnormal profit)
Examiner keyword
The situation where a firm fails to cover all its costs, earning less than normal profit — it occurs when AR < AC (TR < TC).
Profit maximisation
Examiner keyword
Producing the output at which profit is greatest — the output where marginal cost equals marginal revenue (MC = MR), with the price then read off the AR curve.
Shut-down point
Examiner keyword
The output at which a firm just decides whether to keep producing or to stop. In the short run it is where AR = AVC (the minimum of the AVC curve); in the long run it is where AR = AC.
Short-run shut-down condition (AR ≥ AVC)
Examiner keyword
In the short run a firm keeps producing as long as price (AR) covers average variable cost (AR ≥ AVC), so it contributes towards its unavoidable fixed costs and minimises its loss. If AR < AVC it shuts down.
Long-run shut-down condition (AR ≥ AC)
Examiner keyword
In the long run all costs are variable, so a firm stays in the market only if price covers all its costs (AR ≥ AC, at least normal profit). If AR < AC it leaves the industry.
Economic profit
Examiner keyword
Total revenue minus all costs, including implicit costs / opportunity cost (normal profit). Positive economic profit is supernormal profit; zero economic profit means normal profit is being earned.
Accounting profit
Examiner keyword
Total revenue minus explicit (money) costs only, such as wages, materials and rent paid. It ignores opportunity cost, so it is larger than economic profit.
Average variable cost (AVC)
Total variable cost per unit of output (TVC ÷ Q). It is the cost used in the short-run shut-down rule, because variable costs are the costs a firm can avoid by stopping production.
Role of profit
Examiner keyword
In a market economy, profit signals where resources should move (supernormal profit attracts entry, losses cause exit), incentivises efficiency and innovation, rewards risk-taking, and provides retained funds for investment.

Common Mistakes and Misconceptions — Profits and losses (Revenue, Costs and Profits)

The traps other students keep falling into on profits and losses (revenue, costs and profits) questions — taken from recent Pearson Edexcel IAL XEC11 / YEC11 examiner reports and mark schemes — and how to avoid them.

✕Treating normal profit as 'zero profit' or as a loss (thinking the firm makes no money)
WEC13 Examiner Reports
Why it happens
Students hear 'normal profit is where TR = TC' and assume the firm earns nothing.
How to avoid it
Normal profit is a positive reward — the opportunity cost of enterprise — counted as a COST and included in AC. When AR = AC the firm earns NORMAL profit (fine, just no supernormal surplus). 'Zero ECONOMIC profit' and 'normal profit' are the same thing.
✕Claiming supernormal profit when AR only equals AC (or drawing the profit rectangle when AR = AC)
WEC13 mark schemes
Why it happens
Students forget that normal profit is already inside AC, so a surplus needs AR strictly above AC.
How to avoid it
Supernormal profit requires AR > AC. If AR = AC there is only NORMAL profit and no rectangle; if AR < AC it is a LOSS. Check the vertical gap between AR and AC at the profit-maximising output.
✕Using ATC (average total cost) instead of AVC in the short-run shut-down rule
WEC13 Examiner Reports — a recurring error
Why it happens
Students apply the long-run 'cover all costs' idea to the short run without spotting that fixed costs are unavoidable there.
How to avoid it
In the SHORT run compare AR with AVC (produce if AR ≥ AVC), because fixed costs are paid anyway; use AC/ATC only for the LONG-run decision (stay if AR ≥ AC).
✕Getting the profit-maximising rule wrong (e.g. saying maximise TR, or produce where AR = AC)
WEC13 Examiner Reports
Why it happens
Revenue maximisation (MR = 0) and break-even (AR = AC) get confused with profit maximisation.
How to avoid it
Profit is maximised where MC = MR. Revenue is maximised where MR = 0; AR = AC is the break-even (normal profit) point. These are three different outputs — keep them separate.
✕Reading the price off the MR curve instead of the AR curve on the profit diagram
WEC13 Examiner Reports — recurring diagram error
Why it happens
Because MC = MR is used to find the output, students carelessly read the price at the same MR height.
How to avoid it
Use MC = MR only to find the OUTPUT Q*. Then go straight UP from Q* to the AR (demand) curve to find the price P*. The price is always on AR, never on MR.
✕Confusing profit with revenue (calling TR the profit)
WEC13 Examiner Reports
Why it happens
Both are money figures, so students stop at total revenue when a question asks for profit.
How to avoid it
Profit = TR − TC — you MUST subtract total cost. A large revenue can still be a loss. In a profit question, always bring in both revenue and cost.