Question 70

If the radius of the circle is decreased by 10%. The percentage decreased in its areas is :

Solution

Let radius initially = $$r=10$$ cm

=> Area = $$A=\pi(r)^2=100\pi$$ $$cm^2$$

=> New radius after 10% decrease = $$r'=10\times\frac{90}{100}=9$$ cm

=> New area = $$A'=\pi(9)^2=81\pi$$ $$cm^2$$

$$\therefore$$ % decrease in area = $$\frac{100\pi-81\pi}{100\pi}\times100=19\%$$

=> Ans - (C)

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