Question

In the given figure, the area enclosed between the two concentric circles is 770 cm². If the radius of the outer circle is 21 cm, calculate the radius of the inner circle.

Answer 1

Let the Radius of inner circle be r.

Area between concentric circles = area of outer circle – area of inner circle

⇒ 770 =`22/7`(21² − r²)

⇒ (21)² − (r²) = `(770 xx 7)/22`

⇒ 21² − r² = 35 × 7 = 245

⇒ 441 – 245 = r²

⇒ r = `sqrt(196)` = 14 cm

Radius of inner circle = 14 cm.