The area enclosed between two concentric circles is 770 cm². If the radius of the outer circle is 21 cm, calculate the radius of the inner circle.
Mensuration
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Question

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

KnowledgeBoat · Accepted Answer

Let radius of inner circle be r cm. Given, Area enclosed between two concentric circles is 770 cm2 Area enclosed between two concentric circles = Area of bigger circle - Area of smaller circle ⇒ 770 = π(21)2 - πr2 ⇒ 770 = 441π - πr2 ⇒ 770 = (441 - r2) ⇒ 441 - r2 = ⇒ 441 - r2 = 35 × 7 ⇒ 441 - r2 = 245 ⇒ r2 = 441 - 245 ⇒ r2 = 196 ⇒ r = = 14 cm. Hence, radius of inner circle = 14 cm.

Mathematics

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

Mensuration

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