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IB DP Maths AA · Exam special · SL & HL · from the Nov 2024 and May 2025 subject reports · ~12 min read

IB Maths AA Exam Traps: 57 Mistakes Examiners Flagged

57 mistakes IB examiners flagged in the November 2024 and May 2025 Maths AA subject reports, grouped by topic, each with the fix, plus a last-week checklist.

Accuracy & roundingGDC habitsShow that & henceFunctionsCalculusKinematicsProbability & statisticsTrigonometry
RSby Riyaz Sir
mentorriyaz.in
No tag = SL and HLHL ONLY HL students onlyFORMULA BOOKLET given in the examM1A1 how marks are awardedhighlight = comes up again and againHANDY worth memorisingTest yourself at the end

In 30 seconds

  • These are not guesses. Every trap below was named by IB examiners in the Maths AA subject reports for November 2024 and May 2025 (all time zones, SL and HL).
  • Most of the lost marks are habits, not hard maths. Premature rounding, the wrong angle mode, unfinished answers and "show that" done backwards appear in almost every report.
  • How to use this note: read one section a day in the last two weeks. For each trap, say the fix out loud, then try the quick check at the end.

By the end you can

  • Spot the 57 most common ways IB Maths AA students lose marks.
  • Replace each one with the habit examiners want to see.
  • Use a last-week checklist before Paper 1, Paper 2 and (HL) Paper 3.

1Accuracy and presentation

Common mistakeRounding too early. Rounding an intermediate value (say to 3 s.f.) and using it later throws the final answer off. Examiners call this the most common lost mark on Paper 2. Fix: store values in the GDC memory and round only the final answer.
Common mistakeFinal answers to 2 significant figures. IB wants exact answers or 3 s.f. unless told otherwise. A bare 2 s.f. answer loses the A1 mark. Fix: write the unrounded value, then the 3 s.f. answer.
Common mistakeMissing a different accuracy instruction. "Give your answer to two decimal places", "to four significant figures", "as a percentage" or "to the nearest integer" all appeared in May 2025, and many students ignored them. Fix: underline accuracy instructions during reading time.
Common mistakeUnfinished answers. log₂ 16 left as log₂ 16 (it is 4), 0.2/0.35 left as a fraction of decimals (it is 4/7), p + p + p left unsimplified. Fix: simplify anything that obviously simplifies; fractions need integers top and bottom.
Common mistakeMissing brackets. (2n)² written as 2n², subtracting a bracket without changing every sign, (−b)² typed as −b². Examiners singled this out in Nov 2024 and May 2025. Fix: always write the bracket, then expand.
Common mistakeAsymptotes not written as equations. "3/2", "HA = 3/2" or "y ≠ 3/2" are not accepted. Fix: write y = 3/2 and x = −1.
Common mistakeSketches missing what was asked. Intercepts, the vertex, asymptotes or end points left off, or curves drawn outside the domain. Fix: before you sketch, list the features the question names, then label every one with coordinates.

2Using the GDC (Paper 2 and HL Paper 3)

Common mistakeDegree mode in a radians question (or the reverse). Examiners saw kinematics, trig models and integrals worked in degrees in May 2025, and the final mark was lost each time. Fix: check the mode at the start of every trig or calculus question; AA calculus is always in radians.
Common mistakeDoing by hand what the GDC does in seconds. Simultaneous equations, an equation in one unknown, the mean of a frequency table, a derivative at a point, a definite integral: examiners repeatedly saw long algebra and lost time. Fix: "in Paper 2, once you have an equation in one variable, the next mark is for the answer". Use the solver. See GDC guide.
Common mistakeinvNorm with the wrong tail. Typing invNorm(0.88) when the question needs the 6% tail on each side. Fix: sketch the normal curve, shade the region, and enter the area to the left of the value (or use the tail setting).
Common mistakeWriting "from GDC" with no setup. If the answer is wrong, there is nothing to give method marks for. Fix: write the equation you solved, the distribution and its parameters, or the integral with limits, then the answer.

3"Show that", "hence" and reasoning

Common mistakeWorking backwards from the given answer. Substituting the given value to check it, or starting from the answer, scores nothing. Fix: start from what you know and finish with the given result as your last line.
Common mistakeNot laying out a proof LHS → RHS. Cancelling on both sides like scratch work is not a proof. Fix: write the full LHS, transform it step by step, and end with the RHS.
Common mistake"Show that" a 3 s.f. value without more digits. To show θ = 57.3°, you must show 57.29…° first. Fix: give at least one more significant figure than the answer you're showing.
Common mistakeIgnoring "hence". Integrating from scratch after part (i) gave you the identity you needed, or finding an inverse when part (c) already gave the asymptotes. Fix: "hence" means use the previous part. Look for the link.
Common mistakeUsing a later part to answer an earlier one. Not allowed unless the question says so.
Common mistakeRejecting a value without a reason. Crossing out an extra solution earns nothing. Fix: write why it fails, for example "x = −2 is rejected because ln(x − 1) is undefined".
Common mistakeTesting a few values instead of proving. Showing (2n + 5)² − (2n − 5)² is a multiple of 10 for n = 1, 2, 3 earns zero. Fix: expand algebraically for general n, then explain why the result is a multiple of 10.
Common mistakeLeaving earlier parts blank and giving up. Later parts often give you the result you need. Fix: attempt every part; use the "show that" answer in the next part even if you couldn't show it.

4Functions and algebra

Common mistakeDomain of f⁻¹. Forgetting that the domain of f⁻¹ is the range of f, and missing that f(−3) = −1 means f⁻¹(−1) = −3.
Common mistakeRange after a transformation with a restricted domain. Fix: sketch the transformed graph on its domain and read the lowest and highest y-values.
Common mistakeDescribing transformations loosely. "Moved" or "stretched" without direction, factor or vector. Fix: "a horizontal stretch, scale factor ½" and "a translation by (3, 0)" (or the vector).
Common mistakeQuadratic inequalities. Finding the critical values correctly, then writing the wrong inequality. Fix: sketch the parabola and read off where it is above or below the axis.
Common mistakeDiscriminant applications. Missing that "quadratic > 0 for all x" means Δ < 0 with a positive leading coefficient, or that two roots of the same sign need a positive product of roots. Also, for a log to exist the argument must be > 0, not > 1.
Common mistakeLog laws. log(a + b) split into log a + log b, or log 2³ written as (log 2)³ instead of 3 log 2.

5Calculus

Common mistakeGradient and angle. The gradient of a line is tan θ, where θ is its angle with the positive x-axis. "Very few" students used this in May 2025 (f′(a) = tan 70°).
Common mistakeGiven P′(t), substituting into P′. To find the population at t = 4 from a rate, you must integrate (with +C and the initial value) or add a definite integral to the starting value.
Common mistakeMissing the chain rule factor. ∫e2x dx missing the ½, ∫1/(2x + 1) dx missing the ½, d/dx of sin(πx) missing π.
Common mistakeForgetting ∫1/x dx = ln ǀxǀ + C, even though it is in the formula booklet.
Common mistakeArea between curves. Splitting into two integrals and making sign errors. Fix: integrate (top − bottom) once, or use ǀf − gǀ on the GDC, and sketch first.
Common mistakeVolumes of revolution. Forgetting π, or (HL) using the x-axis formula for a rotation about the y-axis. The y-axis formula is in the booklet: V = π∫x² dy.
Common mistakeOptimisation not recognised. "Closest", "greatest", "fastest rate" all mean differentiate (or use the GDC's max/min). The fastest rate of change of h is where h′′ = 0, not where h′ = 0.
Common mistakeUsing the quotient rule for 4x³/3. It's a constant times x³. Simplify before differentiating.
Common mistakeJustifying a minimum. State the sign of f′′ (or the sign change of f′) and say what it means.

6Kinematics

Common mistakeMaximum speed vs maximum velocity. Speed is ǀvǀ. In May 2025 the most common wrong answer to one question was 1.13, the maximum velocity, when the maximum speed was asked for; in another, many found v(5) = −120 but did not say the maximum speed is 120. Fix: graph ǀv(t)ǀ, or compare the largest and smallest values of v.
Common mistakeChange of direction. It happens where v = 0 and changes sign. Students rarely used v = 0.
Common mistakeDistance vs displacement. Distance = ∫ǀvǀ dt (one integral on the GDC). Splitting into pieces is fine, but rounding each piece loses accuracy.

7Probability and statistics

Common mistakeAssuming independence. Multiplying P(A)P(B) when the events were not given as independent. To prove independence, show P(A ∩ B) = P(A)P(B) with numbers.
Common mistakeConditional probability written out of context. "P(A ∣ B)" with no meaning scores no method mark. Fix: write P(age ≥ 75 ∣ age ≥ 55) or P(faulty ∣ positive).
Common mistake"At least", "more than", "fewer than". P(X ≥ 150) is not P(X ≤ 150). Write the inequality in words, then in symbols.
Common mistakeDiscrete distributions. Setting E(X) = 1 instead of ΣP = 1; dividing Σx P(X = x) by n; giving the probability instead of the mode.
Common mistakeFinding μ or σ from two probabilities. Use z = (x − μ)/σ twice with the correct z-values, then solve the two equations.
Common mistakeRegression. The mean point (x̄, ȳ) is where the two regression lines meet; predictions outside the data are unreliable (extrapolation), whatever r is.

8Trigonometry and geometry

Common mistakeThe period of tan. The period of tan(bx) is π/b, not 2π/b. The "vast majority" got this wrong in May 2025.
Common mistakeDividing by cos θ. It loses the solutions where cos θ = 0. Factorise instead, and check every solution is in the interval.
Common mistakeSector area with degrees. A = ½r²θ needs θ in radians.
Common mistake3D problems. Not drawing the right-angled triangle that contains the angle. Fix: redraw it flat in 2D and label it.
Common mistakeBearings and units. Bearings are clockwise from North; convert metres and km before mixing them with a speed.

9Sequences and series

Common mistakeGeometric sequences in context. A ball's 6th bounce height uses n = 6, not n = 5; total distance counts each height twice (up and down).
Common mistakeDiscrete answers. "Rows of cards" or "number of years" must be whole numbers. Don't round 21.4 rows up to 22 when only 21 complete rows fit.

10HL only HL

Common mistakeInduction wording. "Assume n = k" is not an assumption about a statement. Fix: "Assume P(k) is true for some k ∈ ℤ⁺", then show P(k + 1), and finish with a full conclusion.
Common mistakeProof by contradiction. Not negating the statement properly, and cross-multiplying an inequality without saying the quantities are positive.
Common mistakeComplex numbers. Arguments taken from arctan without checking the quadrant; only one square root found; conjugates not written in Cartesian form; GDC conversions between forms not practised.
Common mistakeEuler's method reasoning. Saying the estimate is an overestimate "because it works left to right". Fix: refer to the curve being concave up or down (the tangent lies below or above the curve).
Common mistakeVectors. Writing "L₁ =" instead of r = for a line; using the wrong vectors for the angle between planes.
Common mistakeDifferential equations. Losing the modulus in ln ǀyǀ, or the constant of integration, especially when moduli are involved.
Common mistakeCounting. Using permutations when order doesn't matter, or forgetting to divide by 3! for identical groups.

11Last-week checklist

  • Paper 1: fractions and surds simplified; brackets written; exact values (π/3, √3/2) learned; "show that" starts from the question, not the answer.
  • Paper 2: angle mode checked for every question; values stored, not retyped; 3 s.f. (or the stated accuracy); setup written before every GDC answer.
  • Both: every part attempted; "hence" used; asymptotes written as equations; contexts answered with units.
  • HL Paper 3: read the definitions it gives you; each part builds on the last; use the GDC whenever a part is numerical.
Linking questionFor the calculator skills behind many of these traps, see the GDC guide. To see how many marks these traps are worth, see the grade boundaries.

Test yourself — cover the answers first

Quick check

  1. What accuracy should an answer have if the question doesn't say?
  2. What is the period of tan(2x)?
  3. Which formula do you need for maximum speed rather than maximum velocity?
  4. How should you finish a "show that" question?
  5. To find a population from P′(t), what must you do?
  6. Write the horizontal asymptote 2 correctly.
Show answers
  1. exact, or 3 significant figures
  2. π/2
  3. the maximum of ǀv(t)ǀ
  4. with the given result as the last line
  5. integrate P′(t) and use the initial value
  6. y = 2
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Independent notes written by Riyaz Sir. Not produced, endorsed or approved by the International Baccalaureate Organization. Syllabus codes refer to the IB DP subject guides.