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Is x > y?

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by sanju09 » Wed Sep 15, 2010 3:06 am
Is x > y?

[1] x + y > 0.

[2] x^2 - y^2 > 0.



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Source: — Data Sufficiency |

by Rahul@gurome » Wed Sep 15, 2010 5:39 am
(1) If x = 2 and y = -1, then x > y
If x = -1 and y = 2, then x < y
No unique answer.
So, (1) is NOT SUFFICIENT.

(2) (x - y)(x + y) > 0, implies either (x - y), (x + y) are both positive or both negative.
Case 1: x - y > 0, x + y > 0 implies x > y, x + y > 0.
Case 2: x - y < 0, x + y < 0 implies x < y, x + y < 0.
No unique answer.
So, (2) is NOT SUFFICIENT.

Combining (1) and (2), we have that since x + y > 0, so the first case of statement (2) holds true. Hence, x > y.

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