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If the number of square units in the surface area of a

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Joined: 11 May 2008
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If the number of square units in the surface area of a [#permalink]

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11 Sep 2008, 20:27
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If the number of square units in the surface area of a cylinder with a radius of 6 is 1/2 of the number of cubic units in the cylinder, what is the number of square units in the surface area?

A. 128pi
B. 192pi
C. 216pi
D. 324pi
E. 432pi

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Joined: 29 Aug 2007
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11 Sep 2008, 20:49
arjtryarjtry wrote:
If the number of square units in the surface area of a cylinder with a radius of 6 is 1/2 of the number of cubic units in the cylinder, what is the number of square units in the surface area?

A. 128pi
B. 192pi
C. 216pi
D. 324pi
E. 432pi

$$1/2 (pi r^2 h)$$ = $$2 pi r h + 2 pi r^2)$$
$$(pi r^2 h)$$ = $$2x2 pi r (h + r)$$
$$(r h)$$ = $$4 (h + r)$$
rh = 4 (h + r)
6h = 4 (h + 6)
6h - 4h = 24
h = 12

surface area = 2 pi r (h + r) = 2 pi 6 (12+6) = 216 pi

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Re: SURFACE AREA   [#permalink] 11 Sep 2008, 20:49
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If the number of square units in the surface area of a

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