NECO 2022 · Paper 1 · Q41

Solid mensuration

Find the curved surface area of a cone of height 4 cm and base radius 3 cm, correct to 2 decimal places.

Worked solution (try it first)

Find the slant height by Pythagoras: $l = \sqrt{3^2 + 4^2} = 5$ cm.
The curved surface area is $\pi r l = \frac{22}{7} \times 3 \times 5$ .
That is $\frac{330}{7} \approx 47.14\text{ cm}^2$ , option C.

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