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Question
Find the area of a ring-shaped region enclosed between two concentric circles of radii 20 cm and 15 cm.
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Solution
r1 = 15 cm; r2 = 20 cm
Area of the ring = `pi "r"_2^2 - pi "r"_1^2`
`= pi ["r"_2^2 - "r"_1^2]`
`= 22/7 [(20)^2 - (15)^2]`
`= 22/7 [(20 + 15)(20 - 15)]`
`= 22/7 [35 xx 5]`
`= 110 xx 5`
= 550 cm2
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