WAEC Mathematics 2021 Paper

Concept:For a cone, the curved surface area is given by $\pi r l$, where $r$ is the base radius and $l$ is the slant height.The slant height is found using the vertical height and base radius.Explanation:Given: base radius $r = 8$ cm and height $h = 11$ cm.First, find the slant height using $l^2 = h^2 + r^2$.So, $l^2 = 11^2 + 8^2 = 121 + 64 = 185$.Thus, $l = \sqrt{185} = 13.60$ cm, correct to 2 decimal places.Now, curved surface area $= \pi r l$.Using $\pi = \frac{22}{7}$:Curved surface area $= \frac{22}{7} \times 8 \times 13.60$.This gives $= 341.979...$ cm$^2$.Rounded to 2 decimal places, area $= 341.98$ cm$^2$.Answer:The curved surface area is $341.98\,\text{cm}^2$, correct to 2 decimal places.Therefore, the correct option is A.