WAEC 2018 · Paper 2 · Q13

Probability & distributions

The probabilities that Ali, Baba and Katty will gain admission to college are $\frac23$ , $\frac34$ and $\frac45$ respectively. Find the probability that:

(a)
only Katty and Baba will gain admission;
(b)
none of them will gain admission;
(c)
at most two of them will gain admission.

Worked solution (try it first)

The chances of failing are $\frac13$ , $\frac14$ and $\frac15$ .

(a)

Only Katty and Baba: Ali fails, they succeed: $\frac13 \times \frac34 \times \frac45 = \frac15$ .

(b)

None: $\frac13 \times \frac14 \times \frac15 = \frac{1}{60}$ .

(c)

At most two is everything except all three: $1 - \frac23 \times \frac34 \times \frac45 = 1 - \frac25$
$= \frac35$ .

Report a problem with this question