WASSCE Core Mathematics · Paper 1 style

Sets

One sample question with the full working. 6 more in the app, with instant feedback and repair sessions for the traps below.

In a class of 45 students, 25 study French, 18 study Hausa and 7 study both. How many study neither?

Show the answer and working

Answer: C

n(F ∪ H) = 25 + 18 − 7 = 36. Neither = 45 − 36 = 9.

Trap A Stops one step short of the answer: Before writing the answer, re-read the question's last words (each angle? neither? Ama's share? variance?). Ask: is my number that thing, or a stage on the way to it?

Trap B Double-counts the intersection: n(A∪B) = n(A) + n(B) − n(A∩B). Fill the Venn diagram from the middle outwards.

Trap D Subtracts the overlap twice: n(A ∪ B) = n(A) + n(B) − n(A ∩ B): the overlap was counted twice in n(A) + n(B), so subtract it ONCE. Draw the Venn diagram and fill the middle first.

Traps in Sets

Stops one step short of the answer
Before writing the answer, re-read the question's last words (each angle? neither? Ama's share? variance?). Ask: is my number that thing, or a stage on the way to it?
Double-counts the intersection
n(A∪B) = n(A) + n(B) − n(A∩B). Fill the Venn diagram from the middle outwards.
Subtracts the overlap twice
n(A ∪ B) = n(A) + n(B) − n(A ∩ B): the overlap was counted twice in n(A) + n(B), so subtract it ONCE. Draw the Venn diagram and fill the middle first.
Uses only part of the information
Tick off every number and every condition in the stem as you use it. If one is unticked at the end, the answer is incomplete.

Practise Sets (6 questions)Send to your class on WhatsApp