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

Consider the ring as shown in the figure below,

The inner radius of ring is ‘r’ and the outer radius is ‘R’.

Area of inner Circle = πr2 and Area of outer Circle = πR2

Where r = 12 cm and R = 23 cm

Area of ring = Area of outer circle – Area of inner circle

Area o ring = πR2 – πr2 (put values of r & R)

Area of ring = π(232) – π(122)

Area of ring = π(232 – 122) (taking π common from R.H.S)

Area of ring = π(529 – 144)

= 1210 cm2

Area of ring is 1210 cm2.