Question

Find the area of a flat circular ring formed by two concentric (circles with same centre) whose radii are 9 cm and 5 cm.

Answer 1

The area of the region enclosed by two concentric circles is given by:

$A=\pi (R^2-r^2)$

here $R=9cm,r=5cm$

$A=\frac{22}{7}(9^2-5^2)$

$=\frac{22}{7}(81-25)$

$=176c{m}^2$