Find the surface area of a sphere of radius 10.5 cm?

The correct answer is Option (1) → 1386 cm²

The surface area of a sphere of radius \(r\) is \(4\pi r^{2}\), four times the area of a circle of the same radius. The radius 10.5 cm is \(1.5\times7\), so with \(\pi=\frac{22}{7}\) the 7 cancels and the answer comes out as a whole number.

• Square of the radius: \(r^{2}=10.5\times10.5=110.25\)

• Surface area, taking \(\pi=\frac{22}{7}\): \(\displaystyle 4\times\frac{22}{7}\times110.25=1386\,\mathrm{cm^2}\)