WAEC 2018 · Paper 2 · Q6

(a)
The probability that Kunle solves a particular question is $\frac13$ while that of Tayo is $\frac15$ . If both of them attempt the question, find the probability that only one of them will solve the question.
(b)
A committee of 8 is to be formed from 10 persons. In how many ways can this be done if there is no restriction?

Worked solution (try it first)

Only one solves it: Kunle solves and Tayo doesn't, or Tayo solves and Kunle doesn't.
$\dfrac13 \times \dfrac45 + \dfrac23 \times \dfrac15 = \dfrac{4}{15} + \dfrac{2}{15}$
$= \dfrac{6}{15}$
$= \dfrac25$ .