IB Math Revision Start free
Themed maths

Spot the mistake relay and maths taboo for IB Maths

An end-of-term lesson that is fun and still useful: teams race to find the slip in worked solutions built on the most common exam mistakes, then play maths taboo and pictionary with the course’s vocabulary.

Level
IB Maths SL and HL (AA and AI)
Time
39 minutes, plus a 10-minute extension
Topics
Sequences, trigonometric equations and probability; Radians and the binomial distribution; Accuracy and proof
Equipment
A GDC is useful for task B.

Download student sheet (PDF)Answers (PDF)

Suggested timings

PartTimeWhat
Starter5 minQuick questions on the board
Main: task A12 minRelay, part 1
Main: task B12 minRelay, part 2
Main: task C10 minMaths taboo
Extension10 minFast finishers or homework

Starter (5 minutes)

Spot the slip: each line has one mistake.

  1. The x2 term of (1 + 2x)5 is 10 × 2x2 = 20x2
  2. −32 = 9
  3. ∫ 2x dx = x2

Main activity (34 minutes)

Task A: Relay, part 1 (12 min)

Each worked solution has exactly one mistake. Find it, then give the correct answer.

  1. Find the sum of the first 12 terms of 5, 9, 13, … Working: u12 = 5 + 11 × 4 = 49.
  2. Solve 2 sin x = 1 for 0 ≤ x ≤ 2π. Working: sin x = 1/2, so x = π/6.
  3. P(A) = 0.5, P(B) = 0.4 and P(A ∪ B) = 0.6. Find P(A ∩ B). Working: 0.5 × 0.4 = 0.2.

Task B: Relay, part 2 (12 min)

Each worked solution has exactly one mistake. Find it, then give the correct answer.

  1. Find the arc length of a sector of radius 9 cm and angle 40°. Working: s = rθ = 9 × 40 = 360 cm.
  2. X ~ B(5, 0.5). Find P(X ≥ 1). Working: 1 − P(X ≤ 1) = 1 − 6/32 = 26/32.
  3. Solve 1.08t = 2. Working: t = ln 2 ÷ ln 1.08 = 0.693 ÷ 0.08 = 8.66.

Task C: Maths taboo (10 min)

Describe the word to your team without saying it or any of the banned words.

  1. Describe DERIVATIVE without saying: gradient, slope, differentiate, rate.
  2. Describe ASYMPTOTE without saying: approach, line, touch, infinity.
  3. Describe LOGARITHM without saying: power, exponent, log, base.
  4. Describe RADIAN without saying: degree, angle, pi, circle.

Extension (10 minutes)

For fast finishers.

  1. A student says n2 + n + 41 is always prime, because it is prime for n = 0, 1, 2, 3, 4 and 5. Find the smallest whole number n for which it is not prime.

For teachers

Teacher notes and full worked answers
  • Relay: teams of three. Give each team the first worked solution; when they bring you the mistake and the corrected answer, they get the next one. The first team through all six wins.
  • Every slip here is one of the common mistakes on our AA SL Examiner Insights page, in a new example of our own. Show the page afterwards so students can see which mistakes cost the most marks.
  • Taboo cards: one student describes the word without saying it or any of the banned words; their team guesses. The sample clue on each card shows that it can be done.
  • Pictionary (no words or numbers allowed on the board, 60 seconds each): asymptote, tangent, normal, vector, point of inflection, radian, histogram, box plot.

Starter

  1. 40x2
    • (2x)2 = 4x2, so 10 × 4x2 = 40x2
  2. −9
    • The power is done before the minus: −(32).
  3. x2 + C
    • An indefinite integral needs + C.

Task A: Relay, part 1

  1. 324
    • Mistake: that is the 12th term, not the sum.
    • S12 = 12/2 × (5 + 49) = 324
  2. x = π/6 or 5π/6
    • Mistake: only one solution. sin is also positive in the second quadrant.
    • π − π/6 = 5π/6
  3. 0.3
    • Mistake: assuming independence, which was not given.
    • 0.5 + 0.4 − 0.6 = 0.3

Task B: Relay, part 2

  1. 2π cm
    • Mistake: s = rθ needs θ in radians.
    • 40° = 2π/9, so s = 9 × 2π/9 = 2π
  2. 31/32
    • Mistake: P(X ≥ 1) = 1 − P(X = 0), not 1 − P(X ≤ 1).
    • 1 − 1/32 = 31/32
  3. t = 9.01
    • Mistake: ln 1.08 was rounded to 0.08 too early.
    • t = 0.693147… ÷ 0.076961… = 9.006… = 9.01 (3 s.f.)

Task C: Maths taboo

  1. Sample clue: ‘Tells you how fast y changes as x changes, at each point of a curve.’
    • The word is derivative. Any clue that avoids the banned words is fine.
  2. Sample clue: ‘A straight path that a curve gets closer and closer to but never meets.’
    • The word is asymptote. Any clue that avoids the banned words is fine.
  3. Sample clue: ‘The answer to: how many 10s do I multiply to get 1000? (Three.)’
    • The word is logarithm. Any clue that avoids the banned words is fine.
  4. Sample clue: ‘The size of a turn where the arc is exactly as long as the radius.’
    • The word is radian. Any clue that avoids the banned words is fine.

Extension

  1. n = 40: 1681 = 412
    • Mistake: checking examples is not a proof.
    • n = 40: 1600 + 40 + 41 = 1681 = 41 × 41 (every n from 0 to 39 gives a prime).

The same answers are in the answers PDF. Every answer was recomputed by computer before publishing.

Practise the topics

Maths art maths · Summer escape room maths · Summer puzzle pack maths · All themed maths

More for lessons: Weekly starters · Skill Builders · Free standard lessons · Worksheet builder · Competition maths