The radius of a circle is increased by 10%, then the area is increased by what percent?

The radius of a circle is increased by 10%, then the area is increased by what percent?

A 10%

B 20%

C 21%

D 100%

Solution

Correct Answer: Option C

Area of circle A = π*r2

Increase r by 10% new area is: π*(1.1r)2 = 1.21*π*r2

thus area is increased by (1 - 1.21)

= 0.21

= (0.21*100)%

= 21%