For a 20% decrease in the radius of a circle, what will be the percentage reduction in its area?

A 10%

B 20%

C 36%

D 400%

Correct Answer: Option C

If R is the original radius then the area of the circle is =πr²

If we decrease the radius by 20% the new radius is =0.8r so the new area is=π(0.8r)² = 0.64πr²

Compute the percent of the new to the old: = 0.64πr² / πr²=0.64

The decrease then is 100 - 64 = 36%