JAMB 1993 · UME · Q36

Find the radius of a sphere whose surface area is $154\text{ cm}^2$ . $\left[\pi = \frac{22}{7}\right]$

Worked solution (try it first)

The surface area of a sphere is $4\pi r^2$ : $4 \times \frac{22}{7} \times r^2 = 154$ .
So $r^2 = \dfrac{154 \times 7}{88} = 12.25$ .
Take the square root: $r = 3.5$ cm, option B.