Question 20

If a circle of radius 12 cm is divided into two equal parts by one concentric circle,then radius of inner circle is

Solution

Radius of circle = $$r=12$$ cm

=> Area of circle = $$\pi r^2$$

= $$\pi(12)^2=144\pi$$

If circle is divided into two parts, thus area of inner circle = $$\frac{144\pi}{2}=72\pi$$

Let radius of inner circle = $$r_1$$ cm

=> $$\pi(r_1)^2=72\pi$$

=> $$r_1=\sqrt{72}=6\sqrt{2}$$ cm

=> Ans - (C)

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