WAEC 2019 · Paper 1 · Q28

Plane mensuration

Find the angle which an arc of length $22\text{ cm}$ subtends at the centre of a circle of radius $15\text{ cm}$ . $\left[\text{Take }\pi = \frac{22}{7}\right]$

Worked solution (try it first)

The circumference is $2 \times \frac{22}{7} \times 15 = \frac{660}{7}$ cm.
The angle is the arc's share of $360^\circ$ : $\theta = \frac{22}{660/7} \times 360$
$= \frac{154}{660} \times 360$ .
So $\theta = 84^\circ$ , option B.

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