Question

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

Answer 1

r₁ = 15 cm; r₂ = 20 cm

Area of the ring = `pi "r"_2^2 - pi "r"_1^2`

`= pi ["r"_2^2 - "r"_1^2]`

`= 22/7 [(20)^2 - (15)^2]`

`= 22/7 [(20 + 15)(20 - 15)]`

`= 22/7 [35 xx 5]`

`= 110 xx 5`

= 550 cm²