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if x and y are integers and x > 0, is y > 0?

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Radar
 Post subject: if x and y are integers and x > 0, is y > 0?
 Post Posted: Sun May 25, 2008 4:32 pm 
if x and y are integers and x > 0, is y > 0?

1) 7x - 2y >0
2) -y < x







Ans: E
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GMAT700
 Post subject:
 Post Posted: Thu May 29, 2008 9:36 pm 
1) 7x-2y>0

7(8)-2(3) = positive
7(8)-2(-3) = positive

y can be neg or pos. NOT sufficient.

2) -y<x

x = 8 , y can equal 3
x = 8, -3<8, so y can be positive

x = 8, y can equal -3
x=8, -(-3)<8, 6<8, y can be negative too. Not sufficient.

c) combined: Look at the breakdown from statement (1) with numbers that also satisfy statement (2)'s criteria. y can be neg OR positive.

Answer is Choice E.
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Sudhan
 Post subject:
 Post Posted: Sun Jun 01, 2008 5:56 pm 
BDACE Grid,

From B,
-y<x

Since y is negative, we can swap the signs to make it positive.Hence,
x>y.

X >0 but y can be either -ve integer or +ve integer. Hence Insuff.

From A,
7x-2y>0
--> 7x>2y. X >0, y can be -ve or +ve. Hence Insuff.

From A and B, we can say y can be either +ve or _ve.

Hence E.
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RonPurewal
 Post subject:
 Post Posted: Thu Jun 05, 2008 5:43 am 
Offline
ManhattanGMAT Staff


Posts: 7146
one very important note to the post above:

Sudhan wrote:
From B,
-y<x

Since y is negative, we can swap the signs to make it positive.Hence,
x>y.


actually, you don't know that the quantity (-y) is negative: if y itself is a negative number, then (-y) is positive, and if y itself is positive, then (-y) is negative.
you must take care NOT to assume that (-y) is necessarily a negative quantity; that only has to be the case if y is positive.
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