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Is x>y?

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Is x>y? [#permalink] New post 20 Aug 2013, 21:03
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

56% (01:47) correct 44% (01:07) wrong based on 77 sessions
Is x>y?

(1) x+y>0
(2) x^2-y^2>0

[Reveal] Spoiler:
For 1) x+y>0
x> -y Insufficient

For 2) x^2-y^2>0
x^2>y^2
--> x<-y OR x>y

1) and 2)
x> -y
and x<-y OR x>y

So the answer should be E.
However, the answer key says C. What concept am I missing?

Thanks.

Source of the question is a file that I downloaded from the "Downloads" section here. Advanced GMAT question with readyforGMAT.com on the bottom of the page.
[Reveal] Spoiler: OA

Last edited by Bunuel on 21 Aug 2013, 00:20, edited 2 times in total.
Edited the question.
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Re: Is x>y? [#permalink] New post 21 Aug 2013, 00:27
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Is x>y?

Is x>y? --> is x-y>0?

(1) x+y>0. The sum of two numbers is greater than 0, from this we cannot say which one is greater. Consider (x, y)=(1, 2) and (x, y)=(2, 1). Not sufficient.

(2) x^2-y^2>0 --> x^2>y^2 --> |x|>|y|. Not sufficient. Consider: (x, y)=(-2, 1) and (x, y)=(2, 1).

(1)+(2) From (2) we have that (x-y)(x+y)>0 and from (1) we have that x+y>0, thus x-y>0. Sufficient.

Answer: C.

Hope it's clear.
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Re: Is x>y? [#permalink] New post 21 Aug 2013, 16:05
Bunuel:

Your answer totally makes sense - I'm curious, what led you to immediately jump to X>Y --> X-Y>0? To be honest, if I saw the question in the latter form, my first instinct would be to assume that the real question to be is X>Y?. Appreciate the help!
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Re: Is x>y? [#permalink] New post 22 Aug 2013, 01:41
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mid14 wrote:
Bunuel:

Your answer totally makes sense - I'm curious, what led you to immediately jump to X>Y --> X-Y>0? To be honest, if I saw the question in the latter form, my first instinct would be to assume that the real question to be is X>Y?. Appreciate the help!


Hard to say. When I see x>y, I automatically see x-y>0. Guess it comes with practice.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: Is x>y?   [#permalink] 22 Aug 2013, 01:41
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