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Source: — Data Sufficiency |
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by asamaverick » Wed May 19, 2010 6:42 am
A it is IMO
1) x > [y] , This means x is a positive number and has absolute value greater than that of y. This is enough to say that x^2 - y^2 > 0.

2) [x] > y
consider the examples x = -3, y = 2 => x^2 - y^2 > 0
x = -4, y = -5 => x^2 - y^2 < 0
Hence option 2 is not enough to determine the answer.
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by [email protected] » Thu May 20, 2010 1:22 am
asamaverick wrote:A it is IMO
1) x > [y] , This means x is a positive number and has absolute value greater than that of y. This is enough to say that x^2 - y^2 > 0.

2) [x] > y
consider the examples x = -3, y = 2 => x^2 - y^2 > 0
x = -4, y = -5 => x^2 - y^2 < 0
Hence option 2 is not enough to determine the answer.
x^2 - y^2 > 0? => (x+y)(x-y) > 0? => x+y>0? or x-y>0?

1) x>|y| => x-|y|>0 => x-y > 0 or x+y >0 sufficient

2)|x| > y => |x|-y > 0 => x-y>0 or -x-y>0

but -x-y > 0 implies x+y<0 insuffient

ANSWER (A)
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