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sud21 GMAT Destroyer! Default Avatar
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word problem Post Thu Jan 19, 2012 11:17 pm
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  • Lap #[LAPCOUNT] ([LAPTIME])
    There are some green balls and blue balls in a box. what is the total number of the balls?
    1) The number of the green balls is 1/3 of the number of the total balls
    2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.

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    sam2304 GMAT Titan
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    Post Fri Jan 20, 2012 5:16 am
    Quote:
    There are some green balls and blue balls in a box. what is the total number of the balls?
    1) The number of the green balls is 1/3 of the number of the total balls
    2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.
    1.No info about total balls. All we know is the ratio. INSUFF.
    2.No info about blue balls/total balls. INSUFF.

    Combining 1 & 2, we can get no of green balls with 2 and with both we can get the total balls.

    IMO C.

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    Brent@GMATPrepNow GMAT Instructor
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    Post Fri Jan 20, 2012 6:12 am
    sud21 wrote:
    There are some green balls and blue balls in a box. what is the total number of the balls?
    1) The number of the green balls is 1/3 of the number of the total balls
    2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.
    Let G = # of green balls
    Let B = # of blue balls

    Rewrite target question as "What is the value of G + B?"

    Statement 1:
    G = (1/3)(G+B)
    To simplify, multiple both sides by 3 to get: 3G = B+G
    Simplify to get: 2G-B = 0
    Since we cannot find the value of G+B, statement 1 is NOT SUFFICIENT

    Statement 2:
    G-1 = (1/5)(G-1+B)
    To simplify, multiple both sides by 5 to get: 5G-5 = G-1+B
    Simplify to get: 4G-B = 4
    Since we cannot find the value of G+B, statement 2 is NOT SUFFICIENT

    Statements 1 & 2:
    We now have two equations (2G-B = 0 and 4G-B = 4), which we could solve for G and B
    As such, we now have SUFFICIENT information to find the value of G+B

    Answer = C

    Cheers,
    Brent

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