WAEC 2021 · Paper 2 · Q13

(a)
There are 20 men on a public bus. Of these, 15 wear glasses and 10 wear wrist watches. If one man is chosen at random from the bus, what is the probability that he wears both glasses and wrist watches?
(b)
MNC company buys a car for $27,000.00 and sells it to Mr. Adams for $36,000.00 after a discount of $10\%$ on the marked price. Calculate the: (i) marked price of the car; (ii) percentage profit made by the company.
Separate values with commas, e.g. 3, −2

Worked solution (try it first)

Taking every man to wear glasses or a watch (or both), let $x$ wear both.
Then $15 + 10 - x = 20$ , so $x = 5$ .
The probability that a man chosen at random wears both is $\frac{5}{20} = \frac14$ .

After a $10\%$ discount, Mr Adams paid $90\%$ of the marked price: $0.9 \times \text{marked price} = \text{\textdollar}36,000$ , so the marked price is $\frac{36\,000}{0.9} = \text{\textdollar}40,000.00$ .

The company bought the car for $27,000 and sold it for $36,000, a profit of $9,000.
Percentage profit $= \frac{9000}{27\,000} \times 100$
$= 33\frac13\%$ .