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Question
Find the circumference of the circle whose area is 25 times the area of the circle with radius 7 cm.
Solution
Area of the circle with radius 7 cm = π r2
`= 22/7 xx 7 xx 7`
= 154 cm2
Area of new circle = 25 x area of the drde with radius 7 cm
= 25 x 154 cm2
= 3850 cm2
Therefore ,
π R2 = 3850
R2 = `3850 xx 7/22`
R2 = 1225
R = 35 cm
Radius of new circle = 35 cm
Circumference of new circle = 2 π R
`= 2 xx 22/7 xx 35`
= 220 cm
Hence, Circumference of new circle = 220 cm
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