DS-16

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DS-16

by desihokie » Fri Jan 18, 2008 12:10 am
powerprep Q
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by StarDust845 » Fri Jan 18, 2008 9:32 am

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by desihokie » Fri Jan 18, 2008 9:50 am
ya, A is right...i got the answer too

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Re: DS-16

by Stuart@KaplanGMAT » Fri Jan 18, 2008 7:43 pm
(1) 3y^2 + 7y = x

If we divide both sides by y, we get:

3y + 7 = x/y

Since we know that y is an integer, we know that 3y + 7 is an integer. Therefore, x/y is an integer (and x is a multiple of y). Sufficient.

note: since we know that y>1, y can't be 0, so we can safely divide both sides by y.

(2) x^2 - x is a multiple of y

we can rewite this as:

x(x-1) is a multiple of y

For this to be true, either x or (x-1) has to be a multiple of y. So, x might be a multiple of y, but it doesn't have to be. Insufficient.

(1) is suff, (2) is insuff... choose (A)
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