Q19 of 68 Page 16

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


Area enclosed between two concentric circle = 770 cm2

Radius of outer circle = 21cm

Let radius of inner circle = r cm


Area enclosed = area of outer circle – area of inner circle

Area enclosed = 770 

π 212 – π r2 = 770

 π (441 – r2) = 770



r = 14 cm

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