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OA: A Why is B insufficient

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OA: A Why is B insufficient [#permalink] New post 08 Feb 2007, 19:15
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OA: A

Why is B insufficient?
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 [#permalink] New post 08 Feb 2007, 19:52
Question: x, y >= 1, Is x = (integer value) * y?

...(1) 3y^2 - 7y = x
y(3y-2) = x
Because y is an integer >=1, (3y-2) will always be an integer. SUFF

...(2) x^2 - x = (integer value) * y; assuming integer value = k

x(x-1) = ky

x = [k/(x-1)] * y

Because [k/(x-1)] could be either integer or fraction number. INSUFF.

A. is the answer.
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Re: Gmatprep - inequality [#permalink] New post 08 Feb 2007, 22:08
joyce wrote:
OA: A

Why is B insufficient?


Is x = ky?

From condition 1 we know y(3y+7) = x ==> x = ky where 3y+7 = k, k will always be an interger as y is an integer hence we proved x =ky sufficient

From condition 2 we know (x^2 - x) = ky ==>ky = x(x-1) ==> x = (k/x-1) * y ==> here k/x-1 will not be an integer and hence not sufficient

Answer is A for me.
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Re: Gmatprep - inequality   [#permalink] 08 Feb 2007, 22:08
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OA: A Why is B insufficient

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