Question

Find the area that is enclosed by two concentric circles whose radii are $2$ cm and $5$ cm.

• A. $27\pi$
• B. $21\pi$
• C. $24\pi$
• D. $14\pi$

Answer 1

The correct option is B $21\pi$

Area of inner circle $A_1$ = $\pi r^2$

Area of outer circle $A_2$= $\pi R^2$

Given r=2cm and R=5cm

therfore

$A_1=\pi 2^2$

$A_2=\pi 5^2$

$A_1=4\pi$

$A_2=25cm$

$A2-A1=25\pi -4\pi =21\pi$

area enclosed by two concentric circles=$21\pi$

Therefore option B is the answer.