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For a certain cylinder, the diameter equals the height.

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For a certain cylinder, the diameter equals the height. If every length in this cylinder is decreased by 60%, then to the nearest integer, by what percent does the volume decrease?

(A) 22%

(B) 40%

(C) 60%

(D) 84%

(E) 94 %

This is how I am doing it but getting the incorrect answer. Can someone please help?

Case 1: Assume diameter = 10 then radius = 5 and height will be 10

Volume = pi*r^2*h = 250pi ---------------------------------------------------------(1)

Decrease height by 60 %

New height = 4

New volume = pi*25*4 = 100pi-----------------------------------------------------(2)

Volume decrease in percent = Old - new / old *100

250 pi - 100 pi/250pi * 100 = 60 % which is not correct.

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