Question

Find the area of a ring shaped region enclosed between two concentric circles of radii $20cm$ and $15cm$.

Answer 1

Given: Radius of outer circle, $R=20cm$

and, Radius of inner circle, $r=15cm$

Area of shaded region $=$ Area of outer circle $-$ Area of inner circle

$=\pi (R{)}^2-\pi (r{)}^2$

$=\pi (20{)}^2-\pi (15{)}^2$

$=400\pi -225\pi$

$=175\pi$

$=175\times \frac{22}{7}$ $[\because \pi =\frac{22}{7}]$

$=25\times 22$

$=550c{m}^2$