Register    Login    Search    Rss Feeds

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


 Page 1 of 1 [ 4 posts ] 



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

In the xy-coordinate plane, line l and linke k intersect...

Author Message
sarahmailings
 Post subject: In the xy-coordinate plane, line l and linke k intersect...
 Post Posted: Mon Nov 01, 2010 6:48 pm 
Offline
Course Students


Posts: 7
DS question from MBA.com CAT #2.

In the xy-coordinate plane, line l and line k intersect at the point (4,3). Is the product of their slopes negative?

(1) The product of the x-intercepts of line l and line k is positive.
(2) The product of the y intercepts of line l and line k is negative.


My approach - I was able to get it down to C or E by picturing possible lines on the graph. However, I got stuck between answer choice C or E. I guessed E (the answer is C). Any thoughts about the right answer is C? I'd love suggestions about quicker ways to work it out.

Thanks in advance!
Top 
mschwrtz
 Post subject: Re: In the xy-coordinate plane, line l and linke k intersect...
 Post Posted: Fri Nov 05, 2010 12:56 am 
Offline
ManhattanGMAT Staff


Posts: 506
Check out these many threads and see whether your answer is in there.

http://www.manhattangmat.com/forums/in-the-xy-coordinate-plane-line-l-and-line-k-intersect-t882.html
Top 
atul.prasad
 Post subject: Re: In the xy-coordinate plane, line l and linke k intersect...
 Post Posted: Sun Nov 14, 2010 3:55 pm 
Offline
Students


Posts: 34
Let the lines L and K be given by the equation:

L => y=mx + c
K => y=nx + k

since both lines intersect(or pass thru) @ (4,3)
we can evaluate c and k in terms of m and n respectively.

so L => y = mx + 3-4m
K => y = nx + 3-4n

evaluating statement 1:
x intercept for L = (4m-3)/m
x intercept for K = (4n-3)/n

If you multiply them you get a fraction dependent on m and n from which you cannot infer anything about the product of slopes

From 2 we know that (3-4m)(3-4n) is -ve
or (4m-3)(4n-3) is -ve
Even here we cannot establish if the product of mn is -ve

But if we combine the 2 statements
1 says (4m-3)(4n-3)/(mn) is positive
From 2 we know that (4m-3)(4n-3) is negative.
Hence for 1 to be true, mn must be -ve
which is exactly what we need to find out.
Top 
jnelson0612
 Post subject: Re: In the xy-coordinate plane, line l and linke k intersect...
 Post Posted: Wed Nov 17, 2010 4:15 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
Thank you everyone!

_________________
Jamie Nelson
ManhattanGMAT Instructor
Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 4 posts ] 





Who is online

Users browsing this forum: No registered users and 1 guest

 
 

 
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: