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Sphere Volume

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Sphere Volume

by mariah » Sun Nov 28, 2010 4:15 am
Sphere Volume Formula: V=4/3*pi*r^3
The surface area of a sphere: S= 4*pi*r2

In terms of S, V=?

oa given is [spoiler]Sr/2[/spoiler]
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by Geva@EconomistGMAT » Sun Nov 28, 2010 6:15 am
I'm sorry, but that doesn't seem right. Plug in S into your OA and see if you reach V=4/3*pi*r^3 :

Sr/2 = 4*pi*r2 *r/2 = 2*pr*r^3 (the 4 and the 2 reduce to leave 2) which is not equal to the Volume formula.

in order to get from S=4*pi*r2 to V=4/3*pi*r^3 :, we'd need to take S and:
1) Multiply by r (to get r^3)
2) divide by 3 (to get the 4/3).

Thus, the answer should be Sr/3.
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by rishab1988 » Sun Nov 28, 2010 9:11 am
My approach was very straight forward:

V = 4/3 *pi *r^3 or (4*pi*r^2)r/3 right?
= Sr/3 [just substituted S for 4pi r^2]
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