Area Ratio of Square and Circle of Equal Perimeter

XAT 2025 · Quantitative Ability & Data Interpretation · Easy · Geometry

Adu and Amu have bought two pieces of land on the Moon from an e-store. Both the pieces of land have the same perimeters, but Adu's piece of land is in the shape of a square, while Amu's piece of land is in the shape of a circle.

The ratio of the areas of Adu's piece of land to Amu's piece of land is:

  1. A.

    1 : 1

  2. B.

    \pi^2 : 4

  3. C.

    1 : \pi

  4. D.

    \pi : 4

  5. E.

    \pi : 2

Answer

D

Explanation

Let the common perimeter be PP. For Adu's square land: Side s=P4  ⟹  AreaAdu=s2=P216s = \frac{P}{4} \implies \text{Area}_{Adu} = s^2 = \frac{P^2}{16}. For Amu's circular land: Circumference 2πr=P  ⟹  r=P2π  ⟹  AreaAmu=πr2=π(P2π)2=P24π2\pi r = P \implies r = \frac{P}{2\pi} \implies \text{Area}_{Amu} = \pi r^2 = \pi \left(\frac{P}{2\pi}\right)^2 = \frac{P^2}{4\pi}.

Ratio of areas = P2/16P2/4π=4π16=π4\frac{P^2/16}{P^2/4\pi} = \frac{4\pi}{16} = \frac{\pi}{4}.

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