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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.
Solution
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.
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