WAEC 2021 · Paper 1 · Q30✱✱

Plane mensuration

A trapezium with parallel sides $10\text{ cm}$ and $21\text{ cm}$ and height $8\text{ cm}$ is inscribed in a circle of radius $7\text{ cm}$ . Calculate the area of the region not covered by the trapezium. $\left[\text{Take }\pi = \frac{22}{7}\right]$

Worked solution (try it first)

Area of the circle: $\frac{22}{7} \times 7^2 = 154\text{ cm}^2$ .
Area of the trapezium: $\frac12(10 + 21) \times 8 = 124\text{ cm}^2$ .
The uncovered region is $154 - 124 = 30\text{ cm}^2$ , option C.

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