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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