Question

What will be the radius of a circle whose area is 9 times the area of another circle with diameter 8cm?

• A. 88 cm
• B. 70cm
• C. 72.51cm
• D. 75.36cm

Answer 1

The correct option is D

75.36cm

Let $r_1$ be the required radius.

Given, $\pi r_1^2$ = 9$\pi r_2^2$ ($r_2=4$, given)

$\Rightarrow$ $\pi r_1^2$ = 9$\pi 4^2$

$\Rightarrow$ $r_1^2$ = 144

$\Rightarrow$ $r_1$ = 12 cm