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by ektamatta » Sat Jun 07, 2008 9:12 pm
i this something is missing in ur question. can u plz tell me the source u got this question?
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by debohaldar » Sat Jun 07, 2008 11:58 pm
Yes, the question appeared in one of the GMAT Prep tests.

That's all the statement says and gives 2,4,8,16,32 as the answer choices.
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by niraj_a » Sun Jun 08, 2008 2:42 am
wierd...as I would have picked 4 as the answer, and here's why -

a) cancel the 2s in num and denom
b) since x * y = 1, then both have to be 1
c) so x + y becomes 2 which ^ 2 = 4
d) so x - y becomes 0 which ^ 2 = 0

i'm not excellent at math so i'm sure i'm making a mistake somewhere. not to mention that i just woke up.

i'd love to see the real explanation for this one.
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by Ian Stewart » Sun Jun 08, 2008 3:50 am
niraj_a wrote: b) since x * y = 1, then both have to be 1
Ah- they could both be 1, but they don't both need to be 1. They could both be -1, for example, or x could be 1/2 and y could be 2.

I think there's a typo in the original question- someone posted about it elsewhere on this forum. I believe, if I remember correctly, that it's supposed to read:

[2^(x+y)^2]/[2^(x-y)^2]

i.e. those terms with x and y are actually in the exponent. Just glancing at that, the answer should, I think, turn out to be 16 if xy=1.
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by debohaldar » Sun Jun 08, 2008 9:30 am
Ian's explanation actually makes sense - it's hard to believe though that there's a typo in GMATPrep software.
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