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GRE Math Challenge #69-If the radius of a circular region
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03 May 2015, 01:23
03 May 2015, 01:23
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Question Stats:
96% (00:40) correct
3% (00:50) wrong based on 33 sessions
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If the radius of a circular region were decreased by 20 percent, the area of the circular region would decrease by what percent?
A. 16%
B. 20%
C. 36%
D. 40%
E. 44%
A. 16%
B. 20%
C. 36%
D. 40%
E. 44%
Re: GRE Math Challenge #69-If the radius of a circular region
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12 Dec 2017, 11:24
12 Dec 2017, 11:24
sandy wrote:
If the radius of a circular region were decreased by 20 percent, the area of the circular region would decrease by what percent?
A. 16%
B. 20%
C. 36%
D. 40%
E. 44%
A. 16%
B. 20%
C. 36%
D. 40%
E. 44%
Let us take the radius as = 10
Therefore the area of the circular region = \(pi * r^2\)
=\(pi *10^2\)
=100pi
Now the radius is decreased by 20 percent
i.e 10-(10 * 0.2) = 8, which is the new radius
Therefore area of the circular region with the new radius = \(pi * 8^2\)
=64pi
Therefore the area of the circular region decreased = \(\frac{(New - old)}{old}\) = \(\frac{(64pi - 100pi)}{100pi}\)= \(-36%\) (The value is negative because the percentage is decreased)
gmatclubot
Re: GRE Math Challenge #69-If the radius of a circular region [#permalink]
12 Dec 2017, 11:24
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