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Surface area of the balloon

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Baldini Senior | Next Rank: 100 Posts Default Avatar
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Surface area of the balloon

Post Tue Apr 28, 2009 3:40 am
The volume of a sphere with radius r is (4/3)πr^3 and the surface area is 4πr^3. If a spherical balloon has a volume of 972π cubic centimeters, what is the surface area of the balloon in square centimeters?

(A) 324
(B) 729
(C) 243π
(D) 324π
(E) 729π

(π = pi)
OA is D.

Can someone please explain how to get to the answer?
thanks

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sacx Master | Next Rank: 500 Posts Default Avatar
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Post Tue Apr 28, 2009 4:49 am
I think surface area should be 4πr^2

We can find the radius of the balloon

(4/3)πr^3 = 972π
r^3 = 972 * 3/4
r = 9

Surface area = 4πr^2 = 4*π*9^2 = 324π

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Neo2000 Legendary Member
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Post Tue Apr 28, 2009 4:50 am
Surface area of a sphere is 4(pi)r^2

You've got volume of a sphere. From that you can find r.

Once you have r, you can find th surface area.

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Baldini Senior | Next Rank: 100 Posts Default Avatar
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Post Tue Apr 28, 2009 5:09 am
Thank you very much for your responses - but just to be sure, I have attached a screenshot of the original question (and will assume it was a typing error).
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