A circular area having a radius 20 cm is divided into two equal parts by a concentric circle of radius 'r'. The value of 'r' will be

5 cm

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10 cm

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\sqrt{2}

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\sqrt{2}

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Solution

The correct option is D 10 $\sqrt{2}$ cm
Area of circle $C_{2} = \frac{1}{2}$ Area of circle $C_{1}$
$∴ π r^{2} = \frac{1}{2} \times π \times 20^{2}$
or $r^{2} = 200$
or $r = 10 \sqrt{2}$

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A circular area having a radius 20 cm is divided into two equal parts by a concentric circle of radius 'r'. The value of 'r' will be

The correct option is D 10 √2 cmArea of circle C2=12 Area of circle C1∴πr2=12×π×202or r2=200or r=10√2

The correct option is D 10 $\sqrt{2}$ cm
Area of circle $C_{2} = \frac{1}{2}$ Area of circle $C_{1}$
$∴ π r^{2} = \frac{1}{2} \times π \times 20^{2}$
or $r^{2} = 200$
or $r = 10 \sqrt{2}$