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are x and y both positive? A: 2x -2y =1 b: x/y > 1 IMo

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Manager
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Joined: 22 Sep 2008
Posts: 117
are x and y both positive? A: 2x -2y =1 b: x/y > 1 IMo [#permalink]

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New post 05 Oct 2008, 03:33
are x and y both positive?

A: 2x -2y =1
b: x/y > 1

IMo E..

A:
X = -3, Y -3.5 x-y = 0.5 =1/2
X = 3 ,Y =2.5 x-y = 0.5 =1/2
So A is not suff.

B:
x = -3 y = -2 x/y =1 .5 >1
x=3 y =2 x/y = 1.5 >1
So B is not suff.

A +B :
not suff.
E

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Joined: 21 Apr 2008
Posts: 456
Schools: Kellogg, MIT, Michigan, Berkeley, Marshall, Mellon
Re: are x and y both positive [#permalink]

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New post 05 Oct 2008, 04:06
Well,

My two cents... C

A
X=1, Y=1/2
X=1/2, Y=0
Not suff.

B
X=3, Y=2
X=-3, Y=-2
Not suff.

A+B
from A, X=1/2+Y

in B, (1/2+Y)/y>1; 1/(2Y)+1>1; 1/(2Y)>0, this happens if and only if Y>0, therefore, X>0

My first thought was E, but the GMAT softprep says C, and I had to look for the right solution...

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Re: are x and y both positive [#permalink]

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New post 05 Oct 2008, 07:53
[quote="vr4indian"]are x and y both positive?

A: 2x -2y =1
b: x/y > 1


from a

x-y = 1/2

thus either

x,y +ve or both negative /y/>/x/ or x +ve and y -ve both are tiny fractions........insuff

from 2

x/y> 1 ( both can be +ve or -ve)...insuff however

rewriting x/y> 1 in the form (x-y)/y > 0

both

x-y = 1/2 ( subs in 2) thus (1/2)/y > 0 thus sure y is +ve consiquently x is +ve too

c is my answer

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Re: are x and y both positive   [#permalink] 05 Oct 2008, 07:53
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are x and y both positive? A: 2x -2y =1 b: x/y > 1 IMo

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