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DS1000 Sec3 #19

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Source: — Data Sufficiency |
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Re: DS1000 Sec3 #19

by shibal » Tue Apr 28, 2009 6:32 am
joyseychow wrote:Does x + y = 0?
(1) xy<0
(2) x^2 = y^2

OA: C

My answer is different from OA. Can someone explain the logic. Thanks.
Lets plug in numbers
(1)
x=2 y=-2 ==> xy<0 and x+y=0
x=2 y=-3 ==> xy<0 however x+y is diff than 0
Stmt 1 - insuff
(2)
From both squares, they can be either positive or negative, therefore x+y won't necessarily be equal to zero
Stmt 2 - insuff

When combining both, we know that xy<0, therefore x or y is negative (if both are negative xy>0).... If x^2=y^2 and one of them is negative we can assume x+y=0
Hence, stmt 1 & 2 together are suff

OA:C
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