A spherical balloon is inflated so that its radius increases from 5 cm to 10 cm. By what factor does its surface area increase?
Show answer & explanation
Correct answer: B
Explanation
Surface area of a sphere = 4πr²
This means the surface area is proportional to r².
The radius changed from 5 cm to 10 cm; that is, the radius doubled.
Therefore, the surface area will become 2² = 4 times.