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DS - numbers

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oks: Senior | Next Rank: 100 Posts; Posts: 54; Joined: Mon Oct 22, 2007 10:24 am; Thanked: 1 times

by oks » Wed May 13, 2009 5:01 pm

If X3Y = 24, what is the value of (X3Y3 – X2Y2)?
(1) X2Y2 = 36.
(2) X3Y2 = 72.

I thought the answer is D, but it's not correct. Thoughts?

OA: B

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Source: Beat The GMAT — Data Sufficiency | Wed May 13, 2009 5:01 pm

DeepakR: Master | Next Rank: 500 Posts; Posts: 158; Joined: Tue Sep 30, 2008 8:47 amFollowed by: 1 member; Thanked: 23 times; GMAT Score:660

by DeepakR » Wed May 13, 2009 5:40 pm

From #1 we can only find x/y i.e.
x^2y^2=36 and x^3y=24 hence dividing we get, x/y=24/36
so its insufficient.

From #2 we have x^3*y^2=72 and substituting x^3*y=24 in the above equation we get x=2 and y=3 with which we can find x^3*y^3-x^2*y^2
so B.) alone is sufficient.

- Deepak

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