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DS Official Quant review ... not sure of answer

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DS Official Quant review ... not sure of answer

by what? » Sun Jun 12, 2011 11:38 pm
If xy > o, does (x-1)(y-1) = 1?

1. x+y = xy

2. x = y

OA says 2 is not sufficient but I think I disagree.

(y-1)(y-1) = 1
y^2 - 2y +1 = 1
Y^2-2y = 0.
y(y-2) = 0.

yes we have 2 answer , y =0 or 2... BUT

plugging back into equation we get (0-1)(0-1) =1 and (2-1)(2-1) =1.

Thus B is sufficient. BTW.. this is from the official quant review so I am rather vary of trying to prove it wrong..
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Source: — Data Sufficiency |
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by Frankenstein » Sun Jun 12, 2011 11:53 pm
Hi,
I think you have misinterpreted the question. You need to check if (x-1)(y-1) = 1 or not.
You have taken the equality and got value for x and plugging the same value trying to prove the same(which you have assumed).
From(2): x=y
So, (x-1)(y-1) = (x-1).(x-1) = (x-1)^2.
If x=2, (x-1)(y-1) = 1
if x=3, (x-1)(y-1) = 4(not equal to 1).
So, we can't say whether (x-1)(y-1) = 1 or not
Insufficient
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