### Question 23

SSC-CGL 2020 Mar 3 Shift 1

A circular park is in the form of a ring of inner and outer circumference 440 m and 506 m. The cost of levelling at Rs. 6 per square meter is?

### Solution in Detail

REMEMEBER: Circumference C and area A of a circle are related by the equation: C² = 4πAArea to be levelled is the difference of areas of the outer and inner circles. We can write

Area = $\displaystyle \frac{506^2}{4\pi} - \frac{440^2}{4\pi}$

$\displaystyle = \frac{1}{4\pi}(506 + 440)(506 - 440)$

Use π = 22/7

Area $\displaystyle = \frac{7}{4 \times 22} \times (946) \times (66)$

$\displaystyle = 4966.5$

$\displaystyle \therefore$ cost $\displaystyle = 6 \times 4966.5 $

= 29799 Rs. Ans!

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