Download clean, printable lists of the most common mistakes students make — so you can fix them before they cost marks.
Each sheet is aligned to its exam board and built from recurring student errors highlighted in examiner reports and mark schemes.
What you get
A topic-by-topic mistakes list with a “do this instead” fix and a quick self-check.
How to use it
Review before past papers, then use the quick checks to catch errors under timed conditions.
Why it works
Many marks are lost on predictable slips: rounding, sign errors, units, and misreading commands.
Coverage by topic
Preview (up to 5 per topic)
42 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Number | Rounding every intermediate step ‘to look neat’ and losing accuracy in multi-mark answers. | Keep calculator precision until the final line; round only when the question asks for d.p. or s.f. | Did you round only at the end? |
| Number | Mixing up significant figures with decimal places. | s.f. counts from the first non-zero digit; d.p. counts digits after the decimal point. | Underline the first significant digit — is your answer to the right s.f.? |
| Number | Standard form errors: wrong power or value of a not between 1 and 10. | Write as a × 10ⁿ with 1 ≤ a < 10; adjust n when you move the decimal. | Is a definitely between 1 and 10? |
| Number | Adding fractions by adding numerators and denominators. | Find a common denominator, then add numerators only. | Would expanding back give the originals? |
| Number | Percentage increase/decrease: calculating change but forgetting the original as the base. | Use (change ÷ original) × 100%, or multiplier method consistently. | Is your ‘original’ the right quantity? |
| Ratio & proportion | Treating a ratio as fractions of the wrong total (e.g. 2:3 without 5 parts). | Add parts for the total; scale each part by (amount ÷ total parts). | Do the parts add up to the whole? |
| Ratio & proportion | Direct/indirect proportion confused in recipe or 'best buy' questions. | Set up equal ratios or unit cost (per gram, per hour) and compare fairly. | Are units consistent across the ratio? |
| Ratio & proportion | Speed–distance–time errors (using wrong operation). | Use s = d ÷ t, d = s × t, t = d ÷ s; convert minutes ↔ hours first if needed. | Does a quick sense-check match (faster ⇒ less time)? |
| Algebra | Expanding double brackets: sign slips on the middle terms. | Multiply every term in the first bracket by every term in the second; then combine like terms. | Substitute x = 1 or x = 0 for a quick check. |
| Algebra | Solving inequalities: multiplying or dividing by a negative without flipping the inequality. | If you multiply/divide by a negative, flip < and >. | Did you flip when using a negative multiplier? |
| Algebra | Rearranging formulae: treating a term stuck in a fraction incorrectly. | Clear denominators first or multiply through; treat what you move as inverse operations. | Does substituting numbers satisfy the original? |
| Algebra | Factorising quadratics: wrong pair of factors for the constant term. | Find two numbers that multiply to c and add to b (for x² + bx + c). | Expand your brackets — do you get the original? |
| Algebra | Simultaneous equations: same operation on only one equation. | Align coefficients then add/subtract to eliminate; or substitute consistently. | Do both (x,y) satisfy both equations? |
| Graphs | Gradient from a graph: confusion between ‘rise over run’ signs. | Pick two clear points; gradient = change in y ÷ change in x (consistent order). | Does a positive slope match your sketch? |
| Graphs | y = mx + c: reading gradient as the x-intercept. | Gradient is m (steepness); c is where x = 0 cuts the y-axis. | When x = 0, is y equal to c? |
| Graphs | Plotting/reciprocals: wrong shape for reciprocal or exponential curves. | Sketch key features (asymptotes, intercepts, increasing/decreasing) before plotting points. | Did you label asymptotes where the spec expects? |
| Geometry & measure | Area vs perimeter: using the wrong formula for compound shapes. | Split into parts; add areas; perimeter is distance around the outside only once. | Count each external edge once? |
| Geometry & measure | Circle theorem: mixing alternate segment with angles in the same segment. | State the correct theorem used and the angles it links to. | Does your angle sum match the theorem diagram? |
| Geometry & measure | Pythagoras in non-right-angled triangles. | Confirm a right angle is present; otherwise use cosine rule if required. | Is there a 90° corner in the triangle? |
| Geometry & measure | Volume: using area formula twice without thickness / height. | Volume = area of cross-section × length (prism); identify consistent units. | Are dimensions all in metres or all in consistent units? |
| Trigonometry | SOHCAHTOA used when the triangle is not right-angled. | Right-angled triangles → SOHCAHTOA; otherwise sine/cosine rule for GCSE. | Is there a right angle in the correct corner? |
| Trigonometry | Using sinθ as opposite ÷ hypotenuse but labelling the wrong side ‘opposite’. | Label relative to the angle you are using; redraw small sketch. | Does your ratio match the angle marked? |
| Probability | Adding probabilities for non-mutually exclusive events without subtracting overlap. | Use P(A∪B) = P(A) + P(B) − P(A∩B) when events can happen together. | Can both happen? If yes, did you subtract overlap? |
| Probability | Tree diagrams: not multiplying along branches for combined events. | Multiply along a path; add mutually exclusive paths to total probability. | Do branch probabilities from a node sum to 1? |
| Probability | Independent vs conditional mixed up in word problems. | Independent: P(A and B) = P(A)×P(B). With ‘given’, use conditional reasoning carefully. | Does the problem replace the sample space after the first event? |
| Statistics | Mean from a frequency table: dividing by the number of rows instead of total frequency. | Use Σ(fx) ÷ Σf; midpoints for grouped data. | Is denominator total frequency? |
| Statistics | Interquartile range: subtracting the wrong quartiles or including extremes. | IQR = Q3 − Q1 from ordered data or cumulative frequency graph. | Did you read off CF graph at 25% and 75% correctly? |
| Statistics | Describing correlation from a scatter graph with vague words only. | State type (positive/negative), strength, and a plausible context-based comment if asked. | Did you avoid saying ‘causation’ without support? |
| Sequences | nth term: assuming arithmetic with a wrong common difference. | Check first differences constant; if yes, nth = a + (n−1)d (arithmetic). | Do n = 1, 2, 3 produce the given sequence? |
| Sequences | Geometric sequences: using add instead of multiply. | Common ratio r = term₂ ÷ term₁; nth = a × r^(n−1). | Does dividing consecutive terms give the same r? |
| Multi-step problems | Answering only the final part and ignoring ‘show that’ or ‘hence’ links. | Use results from previous parts when instructed; show all steps required by marks. | Did you re-read the stem for ‘hence’ or ‘using your answer’? |
| Calculator & notation | Calculator in degrees when the problem uses radians (or mixed). | Set mode to degrees unless the question specifies radians (GCSE usually degrees). | Is the calculator mode shown in your working if required? |
| Calculator & notation | Writing 1/3 as 0.33 and continuing with rounded value incorrectly. | Store exact value in calculator memory or use fractions until the last step. | Would exact fraction answer be better for the mark scheme? |
| Proof & reasoning | ‘Show that’: starting with what you must prove and working backwards. | Start from given facts; derive the result in logical steps unless algebra proves an identity both ways neatly. | Is every step reversible or justified? |
| Vectors | Vector addition as adding magnitudes only. | Add components (column vectors) or use triangle/parallelogram law for directions. | Did you add i and j components separately? |
| Vectors | Confusing displacement with distance. | Displacement is vector; distance is magnitude of displacement (if straight). | Does the question ask for direction as well as size? |
| Bounds & error | Error intervals: wrong inequality direction or wrong rounding rule. | If rounded to nearest 10, half-interval is ±5; write as continuous inequality bounds. | Do your bounds recreate the rounded number? |
| Exam technique | Method marks lost: answer only with no working in multi-step questions. | Show key steps: equation, substitution, and one line before the final answer. | Could an examiner follow your method? |
| Exam technique | Units missing or wrong in final answers (area, volume, speed). | Circle or underline required units in the question; include them in the answer line. | Are units consistent (m vs cm)? |
| Exam technique | Misreading ‘increase by factor of’ as addition. | A factor of k means multiply by k; ‘percentage of’ uses the reference quantity. | Did you reread the question for operation keywords? |
| Exam technique | Leaving answers as unsimplified surds or fractions when the mark scheme expects simplest form. | Cancel common factors; rationalise denominator if required by the scheme. | Is your answer in lowest terms? |
A downloadable list of frequent GCSE Maths errors (calculator and non-calculator), paired with a fix and a “quick check” for timed practice.
Yes — common slips are framed for AQA GCSE Mathematics (8300) papers and mark-scheme expectations. Always confirm tier, formulae sheet and assessment objectives using the latest AQA specification and examiner reports.