Find all School-related info fast with the new School-Specific MBA Forum

It is currently 22 Dec 2014, 07:37

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x!= -y, is (x-y)/(x+y) > 1? 1. x>0 2. y<0 [Edit:

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 05 Feb 2008
Posts: 22
Followers: 0

Kudos [?]: 2 [0], given: 0

If x!= -y, is (x-y)/(x+y) > 1? 1. x>0 2. y<0 [Edit: [#permalink] New post 19 Feb 2008, 23:09
If x!= -y, is (x-y)/(x+y) > 1?

1. x>0
2. y<0
[Edit: Made a mistake posting it previously - its y<0 not y>0)

Answer is E in the Official Guide.

I tried solving it by reducing (x-y)/(x+y) > 1 to
2y<0

In this case, I only have to check if y<0. But this is not the way to solve it. Could someone tell me why. The official guide answer uses substitution of numbers.

Last edited by jjaspirant on 20 Feb 2008, 00:11, edited 1 time in total.
Director
Director
User avatar
Joined: 31 Mar 2007
Posts: 586
Location: Canada eh
Followers: 7

Kudos [?]: 39 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 00:06
Hrmmmmmmmmmm, I'd ideally like to do it with a pen and paper, but from what I see

if x & y are both > 0

then x-y / x+y MUST ALWAYS be less than 1. How the hell is it E?

the numerator is smaller than the denominator.
Intern
Intern
avatar
Joined: 05 Feb 2008
Posts: 22
Followers: 0

Kudos [?]: 2 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 00:13
Yes, my mistake

2. y<0

Still can't I simplify (x-y)/(x+y)>1 down to 2y<0 by cross multiplying the equation? Why is it that we have to move 1 to the other side and simplify?


Incorrect:
(x-y)>(x+y)

Correct:
(x-y)/(x+y) - 1 > 0
Director
Director
avatar
Joined: 05 Jan 2008
Posts: 707
Followers: 2

Kudos [?]: 126 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 00:28
It is a clear E

Let us take values

x y -> first case x =2,y=-1
3/1 is > 1 true

second case x=1,y=-3 now 4/-2 =-2

so the answer is a clear E

and for problems where you can take specific values, I would always go for them

regards,
Pras
_________________

Persistence+Patience+Persistence+Patience=G...O...A...L

SVP
SVP
avatar
Joined: 04 May 2006
Posts: 1937
Schools: CBS, Kellogg
Followers: 19

Kudos [?]: 377 [0], given: 1

Premium Member
Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 01:09
jjaspirant wrote:
Yes, my mistake

2. y<0

Still can't I simplify (x-y)/(x+y)>1 down to 2y<0 by cross multiplying the equation? Why is it that we have to move 1 to the other side and simplify?


Incorrect:
(x-y)>(x+y)

Correct:
(x-y)/(x+y) - 1 > 0


Yes, the reason is that you must sure that x+y is not zero and a negative when you divide or multiple two sides of the inequataion by a variable

(x-y)/(x+y) - 1 = - 2y/(x+y) >0
1. if y<0 and x>-y, ok -2y/(x+y) >0. For example: y<0 so y = -2, x >-y so x> 2 or x = 3. Therefore, -2*(-2)/(3-2) = 4>0

2. if y<0 and x<-y, -2y/(x+y) <0. For example: y=-2, x<-y so x<2 so x = 1. Therefore, -2*(-2)/(1-2) = -4<0

Clearly E
Director
Director
User avatar
Joined: 31 Mar 2007
Posts: 586
Location: Canada eh
Followers: 7

Kudos [?]: 39 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 10:15
Ah ok, that makes sense.

Yeah, just plug the heck out of it.
Manager
Manager
avatar
Joined: 28 Dec 2007
Posts: 132
Schools: Stanford R1, Wharton R1 w/int, Chicago R1, HBS R2
Followers: 3

Kudos [?]: 32 [0], given: 1

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 11:00
Sorry, I'm not totally understanding ppl's responses. Are you saying that the condition x!=-y proves that x-y = -2y?, because I'm not sure that that follows...

Here's how I did it:

(1) if x>0 then y<0. We know x cannot be 1 or 2, since 1! =1 and 2!=2 and this would cause the denominator (x+y) to be zero. In the expression (x-y)/(x+y), the numerator should always be positive (pos - neg), and the denominator will always be negative, i.e. if x=3, y=-(3*2*1)=-6, and 3+(-6)<0. So this establishes that the expression is always negative and therefore not >1. suff.

(2) if y<0 then x>0. Again, x cannot be 1 or 2 without the denominator blowing up. Same situation as before, numerator is always positive and denominator is always negative. suff.

I think it's D.
Director
Director
avatar
Joined: 01 Jan 2008
Posts: 629
Followers: 3

Kudos [?]: 136 [0], given: 1

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 11:17
jjaspirant wrote:
If x!= -y, is (x-y)/(x+y) > 1?

1. x>0
2. y<0
[Edit: Made a mistake posting it previously - its y<0 not y>0)

(x-y)/(x+y) = (x+y-2y)/(x+y) = 1 - 2y/(x+y) > 1 <-> y/(x+y) < 0

y/(x+y) < 0

2: y < 0 then y/(x+y) < 0 <-> x+y > 0

x > 0 and y < 0 are not enough to answer that question. (3,-2) and (2,-3) yield different results -> E
Senior Manager
Senior Manager
User avatar
Joined: 06 Jul 2006
Posts: 295
Location: SFO Bay Area
Schools: Berkeley Haas
Followers: 2

Kudos [?]: 34 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 12:27
StartupAddict wrote:
Hrmmmmmmmmmm, I'd ideally like to do it with a pen and paper, but from what I see

if x & y are both > 0

then x-y / x+y MUST ALWAYS be less than 1. How the hell is it E?

the numerator is smaller than the denominator.


If X & Y were both greater than 0, then X! could not be -ve.
Senior Manager
Senior Manager
User avatar
Joined: 06 Jul 2006
Posts: 295
Location: SFO Bay Area
Schools: Berkeley Haas
Followers: 2

Kudos [?]: 34 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 12:29
prasannar wrote:
It is a clear E

Let us take values

x y -> first case x =2,y=-1
3/1 is > 1 true

second case x=1,y=-3 now 4/-2 =-2

so the answer is a clear E

and for problems where you can take specific values, I would always go for them

regards,
Pras


Also X! = -Y, which means the value of X and Y have to such that X! will be equal to Y.
As per St1 X> 0, hence X! can't be -ve. that means the value of Y has to be -ve, so as to compensate for the other minus.
Senior Manager
Senior Manager
User avatar
Joined: 06 Jul 2006
Posts: 295
Location: SFO Bay Area
Schools: Berkeley Haas
Followers: 2

Kudos [?]: 34 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 12:36
jjaspirant wrote:
If x!= -y, is (x-y)/(x+y) > 1?

1. x>0
2. y<0
[Edit: Made a mistake posting it previously - its y<0 not y>0)

Answer is E in the Official Guide.

I tried solving it by reducing (x-y)/(x+y) > 1 to
2y<0

In this case, I only have to check if y<0. But this is not the way to solve it. Could someone tell me why. The official guide answer uses substitution of numbers.


The answer has to be A.

As per St1: x > 0 and also x! = -y, since x > 0 ==> x! > 0, Hence y has to be -ve.

Now putting this info into the equation (x - (y) ==> x + y will be > 0. and (x + y) (given y is -ve , from our calculation) will of course be less than x - y, This will lead to (x - y) / (x + y) > 1
GMAT Instructor
avatar
Joined: 04 Jul 2006
Posts: 1269
Location: Madrid
Followers: 23

Kudos [?]: 139 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 12:52
This is DS 233 in the OG10, What is said about x and y in the question, x is not equal to - y ? My PDF is blurry
Director
Director
avatar
Joined: 01 Jan 2008
Posts: 629
Followers: 3

Kudos [?]: 136 [0], given: 1

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 13:54
kevincan wrote:
This is DS 233 in the OG10, What is said about x and y in the question, x is not equal to - y ? My PDF is blurry


that is correct. x is not equal to -y so that we wouldn't divide by zero.
GMAT Instructor
avatar
Joined: 04 Jul 2006
Posts: 1269
Location: Madrid
Followers: 23

Kudos [?]: 139 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 14:50
If x+y > 0, (x-y)/(x+y) > 1 iff x -y > x + y i.e. y < 0. (2) gives us this information, but even with (1), we do not know that x + y > 0. Together not sufficient
Senior Manager
Senior Manager
User avatar
Joined: 06 Jul 2006
Posts: 295
Location: SFO Bay Area
Schools: Berkeley Haas
Followers: 2

Kudos [?]: 34 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 15:06
What would be the factorial of a number 0< x < 1 ?

Any thoughts ?
Director
Director
avatar
Joined: 05 Jan 2008
Posts: 707
Followers: 2

Kudos [?]: 126 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 20 Feb 2008, 22:11
Factorial of 0<X<1 should be 1

we know the factorial of 0! is 1

and factorial of 1 is 1 so any number between 0-1 should be 1
_________________

Persistence+Patience+Persistence+Patience=G...O...A...L

Director
Director
avatar
Joined: 30 Jun 2007
Posts: 793
Followers: 1

Kudos [?]: 111 [0], given: 0

Re: Is (x-y)/(x+y) > 1? [#permalink] New post 21 Feb 2008, 01:26
Given: If both x and y are greater than 0, then we can simplify the solution. But, with the given question stem, let’s evaluate:
1. x > 0 does not provide any clue that y < 0 not sufficient
2. y < 0 does not provide any clue for x – not sufficient
Both 1 and 2:
x = 1 Y = -5
(x-y)/(x+y) < 1

On the other hand: X = 5 Y = -1
(x-y)/(x+y) > 1

Two different values – not sufficient
Answer: E
Re: Is (x-y)/(x+y) > 1?   [#permalink] 21 Feb 2008, 01:26
    Similar topics Author Replies Last post
Similar
Topics:
If x#-y, is x-y/x+y > 1? 1.) x > 0 2.) y < 0 These ConkergMat 1 02 Mar 2009, 17:51
If x y, is (x-y)/(x+y) > 1? 1.x>0 2.y<0 GODSPEED 9 06 Oct 2008, 17:10
2 Experts publish their posts in the topic If x is not -y, (x-y)/(x+y) > 1? 1) x > 0 2) y < 0 utgirl826 14 06 Jul 2008, 06:57
If x # -y , is (x-y)/(x+y) > 1 ? 1) x>0 2) y<0 dynamo 2 25 Dec 2007, 10:15
If x not equal to -y, is (x-y)/(x+y) <1>0 (2) y<0 saurster 1 06 Aug 2007, 19:06
Display posts from previous: Sort by

If x!= -y, is (x-y)/(x+y) > 1? 1. x>0 2. y<0 [Edit:

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.