Question

The radius of the outer circle is $3$ units and the radius of the inner circle is $2$ units. What is the area of the shaded ring (annulus)?

• A. $4\pi$
• B. $5\pi$
• C. $9\pi$
• D. $13\pi$

Answer 1

The correct option is B $5\pi$

Let $r_1$ and $r_2$ be radius of outer and inner circle respectively

$\therefore$ Area of outer circle$\left(C_1\right)=\pi (r_1{)}^2$

$=9\pi$

Area of inner circle$\left(C_2\right)=\pi (r_2{)}^2$

$=4\pi$

Area of the shaded ring(annulus) $=C_1-C_2$

$=9\pi -4\pi =5\pi$

Hence, area of annulus is $5\pi$.