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Surface area of the balloon

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Baldini Rising GMAT Star Default Avatar
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Surface area of the balloon Post Tue Apr 28, 2009 3:40 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    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 Really wants to Beat The GMAT! 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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    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.

    Baldini Rising GMAT Star 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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