WAEC 2021 · Paper 1 · Q37

Solid mensuration

A cone has a base radius of $8\text{ cm}$ and height $11\text{ cm}$ . Calculate, correct to two decimal places, the curved surface area. $\left[\text{Take }\pi = \frac{22}{7}\right]$

Worked solution (try it first)

The curved surface needs the slant height: $l = \sqrt{8^2 + 11^2}$
$= \sqrt{185}$
$\approx 13.60$ cm.
Curved surface area: $\pi rl = \frac{22}{7} \times 8 \times \sqrt{185}$ .
That is $341.98\text{ cm}^2$ to 2 decimal places, option A.

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