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Bunuel
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Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
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IMO C

Let the diameter be = 100

Diameter increased by 50% = 150.

Old Area = πd^2 / 4 = 100^2 / 4 = 2500

New Area = πd^2 / 4 = 150^2 / 4 = 5625

Increase = 5625-2500 / 2500 * 100 = 125%
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Bunuel
The diameter of a circle is increased by 50%. The area is increased by

(A) 50%
(B) 100%
(C) 125%
(D) 200%
(E) 250%
\(50 + 50 + \frac{50*50}{100}= 125\), Answer will be (C)
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Bunuel
The diameter of a circle is increased by 50%. The area is increased by

(A) 50%
(B) 100%
(C) 125%
(D) 200%
(E) 250%


I plugged in a convenient value for avoiding fractions and to make calculation easy.

Let, the first diameter \(= 20\).

Then the radius \(= \frac{1}{2}*20= 10\) and area = \(\pi r^2 = \pi 10^2=100\pi\)

50% increase \(=20*\frac{1}{2} = 10 \), Total radius after increase\(= \frac{1}{2}(20+10)=15\)

Then the radius = \(\pi r^2=\pi 15^2 = 225\pi\)

Increase percentage of the area \(=\frac{225-100}{100}*100=125\)%

The answer is \(C\)
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