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is x^3 > y?

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sanju09 GMAT Instructor
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is x^3 > y? Post Mon Mar 12, 2012 3:44 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    If x and y are positive, is x^3 > y?
    (1) √x > y.
    (2) x > y.

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    Anurag@Gurome GMAT Instructor
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    Post Mon Mar 12, 2012 7:23 am
    sanju09 wrote:
    If x and y are positive, is x^3 > y?
    (1) √x > y.
    (2) x > y.
    (1) √x > y
    If x = 4, y = 1, then 2 > 1 and x^3 = 4^3 = 64 > 1. Here x^3 > y.
    If x = 1/4, y = 1/3, then 1/2 > 1/3 and x^3 = 1/64. Here x^3 < y.
    No definite answer; NOT sufficient.

    (2) x > y
    If x = 4, y = 1, then 4 > 1 and x^3 = 4^3 = 64 > 1. Here x^3 > y.
    If x = 1/2, y = 1/3, then 1/2 > 1/3 and x^3 = 1/8. Here x^3 < y.
    No definite answer; NOT sufficient.

    Combining (1) and (2), If x = 4, y = 1, then √x > y and x > y. Here x^3 > y.
    If x = 9/16, y = 1/2, then √x = 3/4. Here √x > y and x > y. Here x^3 < y.
    No definite answer; NOT sufficient.

    The correct answer is E.

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    killer1387 GMAT Destroyer! Default Avatar
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    Post Mon Mar 12, 2012 7:26 am
    IMO E

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    Post Mon Mar 12, 2012 8:17 pm

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