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Find the circumference of the circle whose area is 25 times the area of the circle with radius 7 cm.

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#### Solution

Area of the circle with radius 7 cm = π r^{2}

`= 22/7 xx 7 xx 7`

= 154 cm^{2}

Area of new circle = 25 x area of the drde with radius 7 cm

= 25 x 154 cm^{2}

= 3850 cm^{2}

Therefore ,

π R^{2} = 3850

R^{2} = `3850 xx 7/22`

R^{2 } = 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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