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# If a right circular cylinder’s radius is halved and its height doubled

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Joined: 02 Sep 2009
Posts: 52292
If a right circular cylinder’s radius is halved and its height doubled  [#permalink]

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19 Sep 2018, 20:51
1
00:00

Difficulty:

25% (medium)

Question Stats:

83% (00:43) correct 17% (00:46) wrong based on 35 sessions

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If a right circular cylinder’s radius is halved and its height doubled, by what percent will the volume increase or decrease?

(A) 50% decrease
(B) 0%
(C) 25% increase
(D) 50% increase
(E) 100% increase

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Posts: 376
Re: If a right circular cylinder’s radius is halved and its height doubled  [#permalink]

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19 Sep 2018, 21:52
1
Bunuel wrote:
If a right circular cylinder’s radius is halved and its height doubled, by what percent will the volume increase or decrease?

(A) 50% decrease
(B) 0%
(C) 25% increase
(D) 50% increase
(E) 100% increase

Volume of Right Circular Cylinder of radius r and height h
V=$$\pi*r^2*h$$

New Height $$H=2h$$
New Radius $$R=\frac{r}{2}$$

New Volume
$$V'=\pi*R^2*H$$
$$V'=\pi*\frac{(r^2)}{4}*2h$$
$$V'=\frac{V}{2}$$
Hence the volume decreases by V/2

Answeer: A
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If a right circular cylinder’s radius is halved and its height doubled  [#permalink]

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20 Sep 2018, 03:09
1
Bunuel wrote:
If a right circular cylinder’s radius is halved and its height doubled, by what percent will the volume increase or decrease?

(A) 50% decrease
(B) 0%
(C) 25% increase
(D) 50% increase
(E) 100% increase

Volume of the Cylinder $$= π*r^2*h$$

New Volume $$= π*(\frac{r}{2})^2*(2h) = \frac{π*r^2*h}{2}$$

i.e. New Volume is half of previous volume i.e. Volume decreased by 50%

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If a right circular cylinder’s radius is halved and its height doubled &nbs [#permalink] 20 Sep 2018, 03:09
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