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Detailed notes on The allocation of resources for Cambridge IGCSE Economics, covering key concepts, explanations, examples, and exam-focused revision points.
The producer side of the market. Master the law of supply, the determinants, and the movement-vs-shift distinction — mirror to demand but driven by costs and profit.
Mapped to the Cambridge IGCSE 0455 syllabus (2026).
Price up → quantity supplied up. The mirror of demand.
Supply is the quantity of a good or service producers are willing AND able to provide at each price level, over a given period.
The law of supply. As price rises, quantity supplied rises. As price falls, quantity supplied falls. Ceteris paribus.
Why the law holds — two reasons:
1. Profit motive. A higher price means a higher profit margin per unit (assuming costs unchanged). Existing producers respond by producing more — running extra shifts, working overtime, expanding output.
2. New entrants. A higher price makes the market more attractive. New firms ENTER the market, raising total quantity supplied. Conversely, a falling price drives marginal firms OUT.
The supply curve. Price on the vertical axis; quantity on the horizontal. The curve slopes UP from left to right.
Cambridge tip. Mark schemes for "explain the law of supply" reward EITHER the profit motive OR new entrants for partial credit. BOTH for full marks.
Costs, technology, taxes, subsidies, number of producers.
1. Costs of production. The most important shift factor.
Worked example. Oil price spike → trucking companies' fuel costs rise → curve shifts left for goods that depend on road transport.
2. Technology.
3. Indirect taxes and subsidies.
4. Number of producers in the market.
5. Time period. In the short run, supply may be relatively inelastic (hard to expand quickly). In the long run, more elastic (firms can build new factories, train new workers).
6. Weather (for agricultural goods). Good weather → high yield → curve shifts right. Drought → curve shifts left.
7. Expectations of future prices. If producers expect prices to RISE, they may HOLD BACK current supply (shift left now) to sell later for more.
Cambridge tip. Mark schemes for 8-mark "shift the supply curve" questions expect 4 distinct factors. The most-rewarded are costs, technology, taxes/subsidies, number of firms.
One firm vs all firms. Sum horizontally.
Individual supply is the quantity ONE firm is willing and able to supply at each price.
Market supply is the TOTAL quantity ALL firms in the market are willing and able to supply at each price — calculated by summing individual supply curves HORIZONTALLY at each price level.
Worked example. At $10:
Market supply at $10 = 100 + 80 + 120 = 300 units.
Repeat for every price → market supply curve.
Implication. A market with more firms has higher supply at every price. Entry of new firms shifts market supply right.
Verbatim phrases and definitions Cambridge mark schemes credit.
Supply pairs with demand on every Paper 1 and most Paper 2 questions. Examiner reports flag the same errors as on demand: movement-vs-shift confusion and wrong direction on cost-driven shifts.
Sources: Cambridge IGCSE Economics 0455 syllabus (for examination from 2024 onwards); 0455 Examiner Reports — Paper 1 / Paper 2, 2022-2024; 0455/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on supply, written exactly the way a tutor would explain them at the board.
Question
Define what is meant by 'supply'. (2 marks)
Step-by-step solution
Step 1
'Define' is point-marked (up to 2). Use the precise phrasing.
Step 2
The two parts (1 + 1). Supply is the quantity producers are willing and able to provide (1) at each price over a given period (1).
Answer
Supply is the quantity of a good or service that producers are willing and able to provide (1) at each price level over a given period of time (1).
Examiner tip
'Willing and able to provide at each price' is the mark-scheme idea. Don't confuse supply (quantity offered at each price) with stock (a fixed amount currently held).
Question
Explain the law of supply and give two reasons for it. (4 marks)
Step-by-step solution
Step 1
Law of supply (1 + 1). As the price rises, quantity supplied rises (and vice versa), other things equal — so the supply curve slopes upward.
Step 2
Reason 1 — profit (1). A higher price means more profit per unit, so existing producers supply more.
Step 3
Reason 2 — new entrants (1). A higher price attracts new firms into the market, raising total quantity supplied.
Answer
The law of supply states that as the price of a good rises, the quantity supplied rises (and falls as price falls), other things equal — so the supply curve slopes upward (2). This is because a higher price gives producers more profit per unit, so existing firms supply more, and because the higher price attracts new firms into the market, increasing total supply (2).
Examiner tip
State the positive price–quantity relationship, then two reasons (more profit for existing firms; new firms entering). This is a movement ALONG the supply curve, caused by the good's own price.
Question
Analyse, using a supply diagram, how two factors other than its own price could increase the supply of wheat. (6 marks)
Step-by-step solution
Step 1
Set up the diagram (1). Draw an upward-sloping supply curve S1. An increase in supply shifts the whole curve right to S2 (more supplied at every price).
Step 2
Factor 1 — better technology (up to 3). A new, higher-yield farming method lowers cost per tonne and raises output → farmers supply more wheat at every price → curve shifts right.
Step 3
Factor 2 — a subsidy / lower input costs (up to 3). A government subsidy (or a fall in the price of fertiliser) lowers production costs → supplying wheat is more profitable → supply rises → curve shifts right.
Answer
On a supply diagram, an increase in supply is shown by the curve shifting right, from S1 to S2 (more supplied at every price). First, improved technology: a new higher-yield farming method lowers the cost per tonne and raises output, so farmers supply more wheat at each price, shifting the curve right. Second, a subsidy or lower input costs: a government subsidy, or a fall in the price of an input such as fertiliser, reduces production costs, making wheat more profitable to supply, so supply rises and the curve shifts right. Both factors raise supply without any change in the price of wheat itself.
Examiner tip
6-mark 'Analyse' with a diagram: describe the rightward shift, then two distinct conditions of supply (technology; subsidy/input costs), each as a chain to higher supply. Costs and supply move in OPPOSITE directions — lower costs shift supply right.
Question
Analyse how an increase in the cost of raw materials would affect the supply of a manufactured good. (6 marks)
Step-by-step solution
Step 1
Identify the effect on profit (1). Higher raw-material costs raise the cost of producing each unit, lowering profit at any given price.
Step 2
Chain of reasoning (up to 4). Because each unit is less profitable, producers are willing to supply less at every price → the supply curve shifts left (a decrease in supply); some high-cost firms may even leave the market.
Step 3
Develop the consequence (1). With lower supply, the equilibrium price tends to rise and the quantity traded falls.
Answer
An increase in the cost of raw materials raises the cost of producing each unit, so at any given price the good is less profitable to supply. As a result, producers are willing to supply less at every price, and the supply curve shifts to the left (a decrease in supply); some high-cost producers may even stop supplying altogether. With supply reduced, the equilibrium price of the good tends to rise and the quantity traded falls. The key economic point is that costs and supply move in opposite directions — higher costs reduce supply.
Examiner tip
6-mark 'Analyse': develop the chain (higher input costs → lower profit per unit → less supplied at every price → curve shifts left → price rises). Stating the inverse cost–supply relationship clearly is essential.
Question
Discuss whether or not a government subsidy is the best way to increase the supply of a good such as food. (8 marks)
Step-by-step solution
Step 1
Level-marked evaluation. Argue for a subsidy, then for alternatives/drawbacks, then judge.
Step 2
Why a subsidy helps. It lowers producers' costs → supply rises (curve shifts right) → more food produced and lower prices for consumers; useful for essential goods.
Step 3
Drawbacks / alternatives. Subsidies are expensive (opportunity cost of the tax money); they may make producers inefficient/dependent; alternatives include investing in technology or training, improving infrastructure, or removing regulations.
Step 4
Judgement. A subsidy can raise supply effectively, but it has a cost and may not be best — depends on the government's budget and whether other measures (technology, training) give better long-term results.
Answer
A subsidy can raise the supply of food, but whether it is the best method is debatable. Why a subsidy works: a subsidy lowers producers' costs, so they are willing to supply more at every price — the supply curve shifts right, raising output and helping to lower prices for consumers, which matters for an essential good like food. Drawbacks and alternatives: subsidies are expensive, so the money has an opportunity cost (it could fund healthcare or education); they can make producers inefficient or dependent on government support; and there are other ways to raise supply, such as investing in better technology and training, improving rural infrastructure, or removing unnecessary regulations — which may raise productivity more lastingly. Judgement: a subsidy is an effective way to increase supply quickly, especially for essential goods, but it is not always the best because of its cost and the risk of inefficiency. The best method depends on the government's budget and aims — a subsidy suits short-term needs, while investment in technology and skills may be better for long-term supply growth. So a subsidy is one good option, not automatically the best.
Examiner tip
Level 3 (6–8): the subsidy's cost-lowering effect weighed against its expense/opportunity cost and the alternatives (technology, training, deregulation), with a 'depends on budget / short vs long term' judgement. Bringing in opportunity cost links cleanly to Topic 1.
Question
Discuss whether or not the cost of production is the most important factor affecting the supply of a good. (8 marks)
Step-by-step solution
Step 1
Level-marked evaluation. Argue why costs are very important, why other factors also matter, then judge.
Step 2
Why costs are important. Costs directly affect profit per unit; higher costs reduce supply, lower costs raise it; almost every supply decision depends on costs.
Step 3
Why other factors matter. Technology can transform output; indirect taxes and subsidies shift supply strongly; the number of producers, weather (for farming) and the good's own price all matter; for agriculture, weather may dominate.
Step 4
Judgement. Costs are a major influence on supply, but not always the most important — depends on the industry (e.g. weather for crops, technology for manufacturing).
Answer
Costs of production strongly affect supply, but calling them the most important factor in all cases is debatable. Why costs are very important: costs determine profit per unit, so they are central to how much a firm is willing to supply — higher costs reduce supply (curve shifts left) and lower costs raise it; nearly every supply decision depends on costs. Why other factors also matter: technology can dramatically raise output and cut costs; indirect taxes and subsidies shift supply strongly; the number of producers in the market changes total supply; and for agriculture, the weather (e.g. a drought or good harvest) can matter more than anything else. The good's own price also determines the quantity supplied. Judgement: costs of production are one of the most important influences on supply because they affect profitability, but they are not always the most important — the key factor depends on the industry: for farming, weather may dominate; for manufacturing, technology; for taxed goods, government policy. So costs are crucial but not universally the single most important factor.
Examiner tip
Level 3 (6–8): costs (profitability) weighed against technology, taxes/subsidies, number of producers and weather, with a 'depends on the industry' judgement. Recognising that weather can dominate in agriculture is a strong context-specific point.
High-scoring sample answers for supply on the Cambridge IGCSE 0455 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
Define what is meant by a 'subsidy'. (2 marks)
Model answer
A subsidy is a payment made by the government to producers (1) to encourage production — it lowers their costs, increasing supply and often reducing the price for consumers (1).
Why this scores
One mark for 'government payment to producers', one for the effect (lowers costs / raises supply / lowers price). It shifts the supply curve right — the opposite effect of an indirect tax.
Explain the difference between a movement along a supply curve and a shift of the supply curve. (4 marks)
Model answer
A movement along a supply curve (2 marks) is caused by a change in the price of the good itself — producers move to a different point on the same curve (an extension or contraction in supply). A shift of the supply curve (2 marks) is caused by a change in a condition of supply other than price — such as production costs, technology, indirect taxes/subsidies, or the number of producers — which moves the whole curve left (decrease) or right (increase).
Why this scores
The good's OWN price → movement along; any OTHER factor → shift. Same rule as for demand. Examiner reports flag movement/shift confusion as a frequent error.
Analyse how the introduction of an indirect tax would affect the supply of a good. (6 marks)
Model answer
An indirect tax is a tax on a good or service that producers must pay, so it raises the cost of supplying each unit. Because each unit now costs more to provide, the good is less profitable at any given price, so producers are willing to supply less at every price — the supply curve shifts to the left (a decrease in supply). The size of the shift equals the tax per unit. With supply reduced, the equilibrium price tends to rise (part of the tax is passed on to consumers) and the quantity traded falls. Governments often use indirect taxes deliberately on harmful goods like cigarettes to reduce their supply and consumption. The key point is that an indirect tax adds to costs, so it shifts supply left — the opposite of a subsidy.
Why this scores
6-mark 'Analyse': develop the chain (tax raises cost per unit → less profitable → supply falls → curve shifts left → price rises). Contrasting it with a subsidy (which shifts supply right) shows secure understanding.
Analyse two factors that could cause a decrease in the supply of wheat. (6 marks)
Model answer
A decrease in the supply of wheat is shown by the supply curve shifting to the left (less supplied at every price), and it can be caused in several ways. Factor 1 — bad weather. A drought or flood destroys crops and reduces the yield per hectare, so farmers can supply less wheat at every price, shifting the supply curve left. Factor 2 — higher production costs. A rise in the price of fertiliser, fuel or labour makes growing wheat less profitable, so farmers reduce output and the supply curve shifts left; some may switch to other crops. In both cases less is supplied at each price, so the whole supply curve shifts left, which tends to raise the equilibrium price of wheat. Weather and costs are conditions of supply — they are not the price of wheat itself — which is why they shift the curve rather than cause a movement along it.
Why this scores
6-mark 'Analyse': two distinct conditions of supply (weather; input costs), each developed to a leftward shift. For agricultural goods, weather is a key and examinable supply factor.
Discuss whether or not a fall in the price of raw materials will always increase a firm's supply. (8 marks)
Model answer
A fall in raw-material prices usually raises supply, but 'always' is too strong. Why it usually increases supply: cheaper raw materials lower the cost of producing each unit, so the good becomes more profitable at any given price; producers therefore supply more at every price and the supply curve shifts right — and lower costs may attract new firms into the market too. Why it might not always: supply also depends on other factors that could change at the same time — if wages or energy costs rise, or an indirect tax is introduced, total costs may still increase despite cheaper raw materials; a firm at full capacity cannot produce more in the short run even if costs fall; and if demand is weak, the firm may not want to supply more. Judgement: a fall in raw-material prices usually increases supply because it lowers costs and raises profitability, so the firm is willing to supply more. But it does not always do so — it depends on whether other costs change, on the firm's spare capacity, and on demand. So lower raw-material prices push towards higher supply, but the outcome depends on the other conditions of supply, which means 'always' cannot be accepted.
Why this scores
Level 3 (6–8): the cost-lowering effect weighed against other costs changing, capacity limits and demand, with a 'depends on other conditions / capacity' judgement. Recognising that several supply factors can move at once is the discriminator against 'always'.
Discuss whether or not the number of producers is the most important influence on the supply of a good. (8 marks)
Model answer
The number of producers affects supply, but whether it is the most important influence is debatable. Why it might be most important: more producers in a market means more total output at every price, shifting the supply curve right, while firms leaving the market reduce supply — so the number of firms clearly affects total market supply. Why other factors might matter more: costs of production directly affect how much each firm will supply and are central to every supply decision; technology can transform output per firm; indirect taxes and subsidies shift supply strongly; and for farming, weather can dominate. A market with few producers could still supply a lot if each is highly productive, while many high-cost producers might supply little. Judgement: the number of producers is one important influence on market supply, but it is not usually the most important — costs and technology generally have a larger and more direct effect on how much is supplied, and the key factor depends on the industry. So the number of producers matters, especially for total market supply, but it is rarely the single most important factor.
Why this scores
Level 3 (6–8): number of producers (total market output) weighed against costs, technology, taxes and weather, with a 'depends on the industry; costs/technology usually matter more' judgement. Noting that few highly-productive firms can out-supply many high-cost ones is a sharp evaluative point.
Definitions to memorise and the exact keywords mark schemes credit for supply answers — sharpened from recent examiner reports for the 2026 0455 sitting.
The quantity of a good or service producers are WILLING AND ABLE to provide at each price level over a given period.
As price rises, quantity supplied rises, and vice versa, ceteris paribus.
The specific amount producers wish to provide at a particular price.
A tax on a good or service (e.g., VAT, excise duty) — paid by producers but typically passed on to consumers via higher prices.
A government payment to producers to encourage production or lower prices for consumers.
The traps other students keep falling into on supply questions — taken from recent Cambridge IGCSE 0455 examiner reports and mark schemes — and how to avoid them.
Why it happens
Confusing economic supply with inventory.
How to avoid it
Supply is what producers are WILLING AND ABLE to provide AT EACH PRICE — it varies with price. Inventory/stock is a fixed amount currently held.
0455 Examiner Reports 2022-2024
Why it happens
Forgetting the inverse relationship.
How to avoid it
Costs UP → supply DOWN → curve shifts LEFT. Costs DOWN → supply UP → curve shifts RIGHT. Memorise: costs and supply move in OPPOSITE directions.
Why it happens
Both are government interventions.
How to avoid it
Indirect TAX = adds to cost = shifts LEFT (less supplied at every price). SUBSIDY = reduces cost = shifts RIGHT (more supplied at every price).
The things students keep getting wrong in this sub-topic, answered.