Find the area of a ring whose outer and inner radii are respectively 23 cm and 12 cm.

Let r1 cm and r2 cm be the radii of the outer and inner boundaries of the ring, respectively.
We have:

$r_{1}=23 \mathrm{~cm}$

$r_{2}=12 \mathrm{~cm}$

Now,

Area of the outer ring $=\pi r_{1}^{2}$

$=\frac{22}{7} \times 23 \times 23$

$=1662.57 \mathrm{~cm}^{2}$

Area of the inner ring $=\pi r_{2}{ }^{2}$

$=\frac{22}{7} \times 12 \times 12$

$=452.57 \mathrm{~cm}^{2}$

Area of the ring = Area of the outer ring -">−Area of the inner ring

$=1662.57-452.57$

$=1210 \mathrm{~cm}^{2}$