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# if x is not equal to -y, is x-y/x+y >1? 1. x>0 2.

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Senior Manager
Joined: 10 Mar 2008
Posts: 327
if x is not equal to -y, is x-y/x+y >1? 1. x>0 2.  [#permalink]

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15 Oct 2008, 15:57
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if x is not equal to -y, is x-y/x+y >1?

1. x>0
2. y<0

Question:
For such inequality equations is it best to cross multiply or bring 1 to the opposite side?

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Senior Manager
Joined: 31 Jul 2008
Posts: 270

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15 Oct 2008, 16:07
E for me

i tried keeping different values for x and y such as 1,-1,2,-2,0 etc
Senior Manager
Joined: 10 Mar 2008
Posts: 327

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15 Oct 2008, 16:14
anyone with a different approach?
Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown

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15 Oct 2008, 17:04
vksunder wrote:
if x is not equal to -y, is x-y/x+y >1?

1. x>0
2. y<0

Question:
For such inequality equations is it best to cross multiply or bring 1 to the opposite side?

B

Is x-y/x+y >1?
Since x+y is not equal to ZERO
Is x-y>x+y?
Is y>0?

a. Not Sufficient
b. Answer is No - Sufficient
Senior Manager
Joined: 10 Mar 2008
Posts: 327

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17 Oct 2008, 13:10
OA - E. Could someone please explain as to how to tackle such inequality questions. Thanks!
VP
Joined: 17 Jun 2008
Posts: 1284

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17 Oct 2008, 13:31
vksunder wrote:
OA - E. Could someone please explain as to how to tackle such inequality questions. Thanks!

1)x>0 ,we need to consider values of y<0 and y>0 , here in both cases
results are different ,x+y and x-y changes signs

2) y<0 again with x x-y and x+y change INSUFFI

combine both x>0,y<0 => x-y is always +ve but x+y does change when x>y and x<y hence INSUFFI again !!!

HTH
_________________

cheers
Its Now Or Never

VP
Joined: 17 Jun 2008
Posts: 1476

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17 Oct 2008, 13:34
vksunder wrote:
OA - E. Could someone please explain as to how to tackle such inequality questions. Thanks!

Two approaches:
Approach 1:
1-(x-y)/(x+y) < 0 or 2y/(x+y) < 0 or y/(x+y)<0.

Possible conditions:
y < 0 and (x+y) > 0 or
y > 0 and (x+y) < 0.

Looking at both statements, we do not get the above conditions. Hence, E.

Approach 2:
What we need to find out is whether (x-y) is greater than (x+y).

From stmt1, we know that x is positive. But, no clue about y. y can be positive or negative and accordingly, (x-y) could be greater than, euqal to or less than (x+y). Hence, insufficient.

From stmt2, similar explanation.

Combining the two,
x is positive and y is negative. But, we do not know whether in absolute terms, x is more than y. Hence, (x-y) will be positive, but (x+y) could be positive or negative depending on whether y is smaller than x or not in absolute value. Hence, insufficient.
Retired Moderator
Joined: 18 Jul 2008
Posts: 897

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17 Oct 2008, 13:46
Why doesn't doing it work doing B this way? I went with the same approach.

LiveStronger wrote:
vksunder wrote:
if x is not equal to -y, is x-y/x+y >1?

1. x>0
2. y<0

Question:
For such inequality equations is it best to cross multiply or bring 1 to the opposite side?

B

Is x-y/x+y >1?
Since x+y is not equal to ZERO
Is x-y>x+y?
Is y>0?

a. Not Sufficient
b. Answer is No - Sufficient
VP
Joined: 17 Jun 2008
Posts: 1476

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17 Oct 2008, 14:03
1
Why doesn't doing it work doing B this way? I went with the same approach.

LiveStronger wrote:
vksunder wrote:
if x is not equal to -y, is x-y/x+y >1?

1. x>0
2. y<0

Question:
For such inequality equations is it best to cross multiply or bring 1 to the opposite side?

B

Is x-y/x+y >1?
Since x+y is not equal to ZERO
Is x-y>x+y?
Is y>0?

a. Not Sufficient
b. Answer is No - Sufficient

Multiplication is always a problem with inequality unless we are absolutely sure of sign.

If both x+y and x-y are positive then x-y>x+y
But, if both are negative then, x-y<x+y.

Take the example, x-y=12 and x+y=5
or x-y=-12 and x+y=-5

In both cases, x-y/x+y > 1, but cross multiplication will not be true in both cases.
Director
Joined: 23 May 2008
Posts: 740

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17 Oct 2008, 17:21
1) x>0
insuff

2) y<0
insuff

together

let x=2 and y=-1

2--1/ 2-1=3 so yes

let x=2 and y=-3

2--3/ 2-3 =-5 so no
insuff

therefore E

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: DS &nbs [#permalink] 17 Oct 2008, 17:21
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