Question

The area enclosed between the concentric circles is 770cm2. If the radius of outer circle 21cm. find the radius of inner circle

Answer 1

Radius of outer circle = 21𝑐𝑚

Radius of inner circle = 𝑅₂

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

⇒ 770 =`22/7`(21² − R₂²)

⇒ 21² − 𝑅₂² = 35 × 7 = 245

⇒ 441 – 245 = 𝑅₂²

⇒𝑅₂= `sqrt(196)` = 14 𝑐𝑚

Radius of inner circle = 14cm.