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If x not equal to -y, is (x-y)/(x+y) > 1? (1) x>0 (2)

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If x not equal to -y, is (x-y)/(x+y) > 1? (1) x>0 (2) [#permalink]

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New post 27 Jul 2009, 21:07
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If x not equal to -y, is (x-y)/(x+y) > 1?

(1) x>0
(2) y<0

if i re-arrange the equation in question i get the following:

x-y>x+y, further implying that -y>y, therefore -2y>0 or y<0

So the question after re-phrasing it is asking is y<0?

and using the above i answered the question with B

However the Official answer per the GMAT prep is E

Could someone please explain the methodology so that I can understand as to where I could be going wrong.

thanks in advance.

Best,

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Re: GMAT PREP PROBLEM [#permalink]

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New post 27 Jul 2009, 22:47
uvs_mba wrote:
If x not equal to -y, is (x-y)/(x+y) > 1?

(1) x>0
(2) y<0

if i re-arrange the equation in question i get the following:

x-y>x+y, further implying that -y>y, therefore -2y>0 or y<0

So the question after re-phrasing it is asking is y<0?

and using the above i answered the question with B

However the Official answer per the GMAT prep is E

Could someone please explain the methodology so that I can understand as to where I could be going wrong.

thanks in advance.

Best,


I tried to solve it using 2-3 different methods. But could not. My answer always comes B.

Can you please out explanation given by GMAT prep ? May be then I can help.
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Re: GMAT PREP PROBLEM [#permalink]

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New post 27 Jul 2009, 22:48
uvs_mba wrote:
if i re-arrange the equation in question i get the following:

x-y>x+y, further implying that -y>y, therefore -2y>0 or y<0


Note, you cannot just cross-multiply the numbers in inequalities.
Rule: You can multiply both sides with a +ve number, without changing the sign of inequality. To multiply both sides with a -ve number, inequality sign is reversed.

So, if you intend to simplify the equation (x-y)/(x+y) > 1, there can be two cases
1st, when (x+y) is +ve, then
(x-y)/(x+y) > 1
or (x-y) > (x+Y)
or y < 0

2nd, when (x+y) is -ve, then
(x-y)/(x+y) > 1
or (x-y) < (x+Y) ....notice the sign has been reversed
or y > 0
That means in 2nd case, when y <0 would mean (x-y)/(x+y) < 1
=> when y<0, we have the equation <1 or >1 depending upon the sign of (x+y)

Lets evaluate the options now
1. x>0 -clearly insufficient
2. y<0 -insufficient, as we have already seen in the above calculation.
3. Together: we still cannot determine the sign of x+y, unless we know a relationship between x and y.

IMO E.
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Kudos [?]: 902 [0], given: 56

Director
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Joined: 03 Jun 2009
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Re: GMAT PREP PROBLEM [#permalink]

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New post 27 Jul 2009, 22:50
BTW, an easier way would be by substituting numbers.

E.g. {x, y} = {2, -1} and {2, -4} ....values confirms to the conditions given in both the options
Now, try to resolve the equation, and you'll get the answer :)

The basic idea is, in one example |x| > |y|, and another example when |x| < |y|
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ISB 2011-12 thread | Ask ISB Alumni @ ThinkISB
All information related to Indian candidates and B-schools | Indian B-schools accepting GMAT scores
Self evaluation for Why MBA?

Kudos [?]: 902 [0], given: 56

Re: GMAT PREP PROBLEM   [#permalink] 27 Jul 2009, 22:50
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