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Arithmetic problem - unsure of the solution

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ameya
 Post subject: Arithmetic problem - unsure of the solution
 Post Posted: Mon May 26, 2008 4:12 pm 
If xy = 1, what is the value of : [2(x+y)^2] / [2(x-y)^2]?
Ans: 16

I am unable to get to the solution. I came across this one in the GMAT prep. I guess I am doing something silly!
Please post your solution.

Cheers
~a
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RonPurewal
 Post subject:
 Post Posted: Wed Jun 04, 2008 7:23 am 
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ManhattanGMAT Staff


Posts: 7146
yeah, that problem was mistranscribed in gmatprep for a while. the (x+y)^2 and (x-y)^2 are actually supposed to be exponents, with the 2's as their bases. so it's actually (2 to the power (x+y)^2) / (2 to the power (x-y)^2)

you subtract the exponents, and the squared terms cancel, leaving you with 2 to the power 4xy. that's 2^4 = 16.

there was another thread about this problem, but i can't find it at the moment (it's hard to find problems like this one, which has basically no keywords)
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