DS question : If X # -Y, Is (X-Y)/(X+Y) > 1

[mba012012]

Hi,

Could'nt find a discussion on this question in the forum. Apologies if there is already one. I got this one in the GMAT Prep Practice Test 2.

Question :
If X # -Y, Is (X-Y)/(X+Y) > 1
(1) X > 0
(2) Y < 0

Answer : E

It took me some time to answer this question. How ever I got it as A instead of E . I think I'm messing up while taking the values of X and Y. Could some one please suggest me what pattern should be followed here ? Is there any intuitive approach instead of putting values for X and Y ?

Thanks !

[kourakis]

Question :
If X # -Y, Is (X-Y)/(X+Y) > 1
(1) X > 0
(2) Y < 0

****
I don't think there is an easy algebraic solution, since we don't know the sign of (X+Y), and we can hence NOT cross-multiply. However, you can try to make the numbers positive >1 and negative by picking the right pairs, so that you prove insufficiency.

(1) X>0. Try X=4, Y=-2: (4+2)/(2) = 3 (OK)
Try X=1, Y=2: (1-2)/... no need to calculate since <0 (NG)
INSUFFICIENT

(2) Y<0. Try X= 2, Y=-3: (2+3)/(2-3) < 0 (NG)
Try X=3, Y=-2: (3+2)/(3-2) >1 (OK)
INSUFFICIENT

(1)^(2) Try x=1, y=-10000

(1+10000)/(1-10000) <0 (NG)

Try x=10000, Y=-1
(10000+1)/(9999) >1 (OK)

Therefore E.

Also, I would first try to prove insufficiency with positive/negatives, or extreme integer values, and then I would move to fractions, since computation for the latter is more time consuming.

Finally, I think that this problem could have been solved by drawing a number line. It helps to understand it conceptually..

Hope this helps!

[mba012012]

Thanks Kourakis !

I have a real problem with inequalities :( :(

I don't have an idea on that " Number Line " concept. Could you please suggest me where can i find an explanation for that topic (or) explain me with an example here. It will be really helpful for me because I have my exam date on 24th.

Thanks in advance !

[kourakis]

Watch this:

http://vimeo.com/22453684

A number line helps you test values in a systematic way. Unfortunately I cannot show you how I would do this at this specific problem, because I cannot draw lines here!

Also, given that your exam is in 4 days, I'd recommend you perfect skills you already possess... Testing values is not that hard, as long as you are careful and systematic. Even if it seems like an arbitrary method, it is often the only method you can solve such a problem under 120secs.

Good luck!

[RonPurewal]

here's another thread on this problem
if-x-y-is-x-y-x-y-1-t11432.html