Register    Login    Search    Rss Feeds

Forums Home » Ask An Instructor » GMAT Math » Manhattan GMAT CAT Math


 Page 1 of 1 [ 10 posts ] 



  Print view Print view Previous topic Previous topic | Next topic Next topic
 

manhattan abs value Problem

Author Message
Jimmy
 Post subject: manhattan abs value Problem
 Post Posted: Thu Jul 24, 2008 10:37 pm 
This one is from one of the Manhattan CATs:

What is the value of y?

(1) 3|(x^2) – 4| = y – 2

(2) |3 – y| = 11


Here is how I tackle the problem....

Statement 1) Insuff...But tells us y>= 2 (Got this!)

Statement 2) Insuff...here is where I get lost.

I split the absolute value into two cases:

If Y > 3, THEN y = 14
If Y < 3, THEN y = -8

Now I check both statements. I know y>=2. In these type of abs value problems I now check to see what case I am in. But looking at the IF statements I could be in either case. This is where I am lost. Since both IF statements are valid, do I just move on to checking against the THEN statement? Can a Manhattan genius help out on this one?
Top 
thesamet
 Post subject:
 Post Posted: Fri Jul 25, 2008 1:50 pm 
Since most if's are valid, you need to see if you still can deduce the value of y. The evaluation of the second "if" gives you a contradiction to y>=2, so there's one option left. But...

You made it more complicated than it really is. Look at it that way:

Statement 1 yells you that y>=2.

Statement 2 tells you that y is either -8 or 14.

Neither of them is sufficient but combining them, there's only one option left.
Top 
Guest
 Post subject:
 Post Posted: Mon Aug 11, 2008 5:36 am 
Y=14 is true for y>3

hence the answer shd be E
Top 
RonPurewal
 Post subject: Re: manhattan abs value Problem
 Post Posted: Tue Sep 09, 2008 7:04 am 
Offline
ManhattanGMAT Staff


Posts: 7146
Jimmy wrote:
This one is from one of the Manhattan CATs:

What is the value of y?

(1) 3|(x^2) – 4| = y – 2

(2) |3 – y| = 11


Here is how I tackle the problem....

Statement 1) Insuff...But tells us y>= 2 (Got this!)

Statement 2) Insuff...here is where I get lost.

I split the absolute value into two cases:

If Y > 3, THEN y = 14
If Y < 3, THEN y = -8

Now I check both statements. I know y>=2. In these type of abs value problems I now check to see what case I am in. But looking at the IF statements I could be in either case. This is where I am lost. Since both IF statements are valid, do I just move on to checking against the THEN statement? Can a Manhattan genius help out on this one?


yeah, you're making life too hard for yourself.

here's the deal: |3 - y| = 11 is an EQUATION. equations have SOLUTIONS, which are values that solve them.
that's it.
in particular, any given value either solves the equation or it doesn't. you can't impose "if"s on the issue of whether a given value solves an equation; if it does, it does, and if it doesn't, it doesn't.
it may be true that "if"s are helpful in FINDING the solutions to an equation, but, once you've found those solutions, you can chuck the "if" and just take the solutions.
so:
the equation |3 - y| = 11 has two solutions, -8 and 14.
if you check each of these, you'll find that it works: |3 - (-8)| = 11, check, and |3 - 14| = 11, check.
done.
so statement (2) just means y = -8 or y = 14.
unconditionally.
there's no need to impose inequality-type restrictions; it's just "y is either this or that".
Top 
monira.linda
 Post subject: Re: manhattan abs value Problem
 Post Posted: Sat May 28, 2011 11:38 am 
Offline
Course Students


Posts: 13
I did not get Statement 1 :-(
Y we are assuming |x^2 -4| is greater than zero or equal zero. Y not negative?

Pls help I just have few more days left for my exam...
Top 
jnelson0612
 Post subject: Re: manhattan abs value Problem
 Post Posted: Mon May 30, 2011 1:38 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
monira.linda wrote:
I did not get Statement 1 :-(
Y we are assuming |x^2 -4| is greater than zero or equal zero. Y not negative?

Pls help I just have few more days left for my exam...


Those bars arond x^2 - 4 are absolute value bars. Absolute value means the positive distance between that result and zero. Absolute value can NEVER be negative; the smallest result is zero. Thus, that expression is zero or greater.

_________________
Jamie Nelson
ManhattanGMAT Instructor
Top 
monira.linda
 Post subject: Re: manhattan abs value Problem
 Post Posted: Thu Jun 02, 2011 12:44 am 
Offline
Course Students


Posts: 13
oh got it. Thank u so much :-)
Top 
jnelson0612
 Post subject: Re: manhattan abs value Problem
 Post Posted: Tue Jun 07, 2011 12:29 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
My pleasure! :-)

_________________
Jamie Nelson
ManhattanGMAT Instructor
Top 
monira.linda
 Post subject: Re: manhattan abs value Problem
 Post Posted: Tue Aug 09, 2011 1:24 pm 
Offline
Course Students


Posts: 13
From ST 1 .............. Y>= 2
From ST 2............... Y=14 or -8

Hence, Y=14.

Is the ans C?
Top 
jnelson0612
 Post subject: Re: manhattan abs value Problem
 Post Posted: Sun Sep 11, 2011 11:55 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
The answer is indeed C.

_________________
Jamie Nelson
ManhattanGMAT Instructor
Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 10 posts ] 





Who is online

Users browsing this forum: No registered users and 0 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: