Register    Login    Search    Rss Feeds

 Page 1 of 2 [ 16 posts ] Go to page 1, 2  Next



 
Author Message
 Post subject: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Thu Jul 23, 2009 11:27 am 
Offline
Students


Posts: 28
Hi,

A minor issue in the answer explanation to this problem. I am not copying out the entire explanation.

If x and y are integers such that x < y < 0, what is x - y?

(1) (x + y)(x - y) = 5
(2) xy = 6

Part of the explanation given is

As you can see, the difference between squares grows as the squares themselves get larger. The only difference between two squares that equals 5 is the difference between 4 and 9. Since x and y are both negative, this tells us that x = -3 and y = -2; therefore, x - y = -5.

The bolded portion should be
x - y = (-3) - (-2) = (-3) + 2 = -1


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Fri Jul 24, 2009 1:27 am 
Offline
Forum Guests


Posts: 12
[Attention mbachase.com: we appreciate your desire to help GMAT students. Unfortunately, we don't host posts from competitors on our forums. If you'd like to offer free services to your students (and I think that's a great idea!), then you might consider starting your own forums. Good luck! Stacey]


Last edited by www.mbachase.com on Thu Aug 20, 2009 12:36 am, edited 1 time in total.

Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Tue Aug 18, 2009 1:23 pm 
Offline
ManhattanGMAT Staff


Posts: 818
Hi furtadovinod,

Thanks for the correction. I'll be sure to forward this to the right people so that it gets corrected on our explanations.

_________________
Ben Ku
Instructor
ManhattanGMAT


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Tue Oct 13, 2009 2:13 am 
Offline
Students


Posts: 3
Hi,

I came across the same question in my Manhattan test today and I felt that the answer could be D


If x and y are integers such that x < y < 0, what is x - y?

(1) (x + y)(x - y) = 5
(2) xy = 6

Considering B alone here, [according to this question A is the answer and the explanation is provided - only correction needed x - y = -1]

xy = 6
The options here are -3 and -2
Since we know x<y<0 , x= -3 and y=-2

x - y = -3 - (-2) = -1

which means D should be the correct answer. Manhattan Staff, please let me know if am right?

Thanks,


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Wed Oct 21, 2009 10:57 am 
Offline
Students


Posts: 2
Hey heydharini,

What about x = -6 and y = -1?

This makes xy = 6 as well.

Now you have two different solutions for x-y. So B and D can not be the answers.


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Mon Nov 02, 2009 10:23 pm 
Offline
ManhattanGMAT Staff


Posts: 13509
mkorrapati wrote:
Hey heydharini,

What about x = -6 and y = -1?

This makes xy = 6 as well.

Now you have two different solutions for x-y. So B and D can not be the answers.


correct.

_________________
Pueden hacerle preguntas a Ron en castellano
Potete fare domande a Ron in italiano
On peut poser des questions ã Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

Un bon vêtement, c'est un passeport pour le bonheur.
– Yves Saint-Laurent


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Tue May 25, 2010 11:32 pm 
Offline
Students


Posts: 3
I got the answer right by accident I guess; I surmized that x^2-y^2 =5 thus x-y= +/- sq. root 5. Knowing x and y are both negative and x is farther away from zero x-y must = neg. sq. root 5. I'm still not seeing why this is wrong. Please correct me and explain the answer


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Sun Jun 06, 2010 3:09 pm 
Offline
Students


Posts: 87
The term is [(x^2) - (y^2)] and not (x-y)^2.

You cannot take square root for the left hand side i.e. for

[(x^2) - (y^2)].

I hope that helps.

Aditya.


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Wed Jun 23, 2010 9:30 am 
Offline
ManhattanGMAT Staff


Posts: 13509
adiagr wrote:
The term is [(x^2) - (y^2)] and not (x-y)^2.

You cannot take square root for the left hand side i.e. for

[(x^2) - (y^2)].

I hope that helps.

Aditya.


yes.

this confusion is going to be a very bad thing on the test, if it persists. therefore, you should probably pick up an algebra book -- or surf the internet -- and look up "difference of squares" and "perfect square trinomials"; these are the two factoring patterns that you are confusing.

you may also want to check out the uses of the distributive property; you are mistakenly applying it to square roots, when in fact it only applies to multiplication and division.

_________________
Pueden hacerle preguntas a Ron en castellano
Potete fare domande a Ron in italiano
On peut poser des questions ã Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

Un bon vêtement, c'est un passeport pour le bonheur.
– Yves Saint-Laurent


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Mon Sep 05, 2011 1:38 am 
Offline
Students


Posts: 47
What is the ans?

BR


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Sat Oct 15, 2011 10:40 pm 
Offline
ManhattanGMAT Staff


Posts: 2649
yousuf_azim wrote:
What is the ans?

BR


The answer is A.

_________________
Jamie Nelson
ManhattanGMAT Instructor


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Fri Nov 11, 2011 9:23 am 
Offline
Students


Posts: 1
Hi Guys,

Is there any way of finding out a solution algebrically?

During the exam testing numbers, always makes one wonder if there may be more solutions?

I understand that x and y are integers so the options for testing numbers is less, but still if there is an algebric solution, it'll be great.

Thanks,
Hassan


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Fri Nov 25, 2011 1:35 pm 
Offline
ManhattanGMAT Staff


Posts: 5074
Location: Southwest Airlines, seat 21C
Hassan, if you are interested in a solution that uses more algebra than what you've already seen in the posts above, that is probably not a good idea. The fact that x and y are integers means that you should factor that into your solution method in order to make things easier. A purely algebraic solution that only restricts x and y to integers at the end would be much less efficient..

_________________
Tim Sanders
Manhattan GMAT Instructor


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Wed Jan 29, 2014 3:32 am 
Offline
Course Students


Posts: 24
(x-y)(x+y)=5

We need to figure out the value for x-y. Couldn't x-y= 1 or 5? So we are not sure about the (x-y) value?

Also if x is smaller than y and y is smaller than 0 then it means that
x must be -4 and y must be -1 to make (x-y)=-5. The question says "x < y < 0".
Then (x+y) will not equal -1 to make a positive 5. This will not happen because one -4 and other is -1. no way, it will equal -1.


Top 
 Post subject: Re: If x and y are integers such that x < y < 0, what is x – y?
 Post Posted: Wed Jan 29, 2014 10:32 am 
Offline
ManhattanGMAT Staff


Posts: 13509
chughbrajesh wrote:
(x-y)(x+y)=5

We need to figure out the value for x-y. Couldn't x-y= 1 or 5? So we are not sure about the (x-y) value?

Also if x is smaller than y and y is smaller than 0 then it means that
x must be -4 and y must be -1 to make (x-y)=-5. The question says "x < y < 0".
Then (x+y) will not equal -1 to make a positive 5. This will not happen because one -4 and other is -1. no way, it will equal -1.


You're correct that x - y doesn't equal -5. Both numbers are negative, so x + y will be more negative (= farther to the left on the number line) than x - y.

Since everything is in terms of integers, that leaves only one possibility: x - y = -1 and x + y = -5. So, sufficient.

(You'll get x = -3 and y = -2, although, as long as you know it guarantees a unique answer, it's unnecessary to solve the system once you've found it).

_________________
Pueden hacerle preguntas a Ron en castellano
Potete fare domande a Ron in italiano
On peut poser des questions ã Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

Un bon vêtement, c'est un passeport pour le bonheur.
– Yves Saint-Laurent


Top 
Display posts from previous:  Sort by  
 
 Page 1 of 2 [ 16 posts ] Go to page 1, 2  Next





Who is online

Users browsing this forum: No registered users and 2 guests

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to: