Question:
The radii of two spheres are in the ratio 1 : 2. Find the ratio of their surface areas.
Solution:
Suppose that the radii are r and 2r.
Now, ratio of the surface areas $=\frac{4 \pi r^{2}}{4 \pi(2 r)^{2}}=\frac{r^{2}}{4 r^{2}}=\frac{1}{4}$
= 1:4
∴ The ratio of their surface areas is 1 : 4.