BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

41) MOD DS

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Legendary Member
Posts: 576
Joined: Sat Mar 13, 2010 8:31 pm
Thanked: 97 times
Followed by:1 members

by liferocks » Tue May 11, 2010 10:20 pm
we can re write the question as
IS (x+y)(x-y)>0

From 1 x>|Y|

hence X is positive ..so (x+y) and (x-y) will be both positive...(x+y)(x-y)>0 ..sufficient

From 2
|x|>y
Image

So (x+y)(x-y)>0 ..sufficient
Ans option D
"If you don't know where you are going, any road will get you there."
Lewis Carroll
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 66
Joined: Tue Dec 15, 2009 3:07 am
Location: Bangalore
Thanked: 9 times
GMAT Score:730

by ballubalraj » Wed May 12, 2010 1:06 am
Another way to solve it:

Square of any positive or negative number is always positive. So irrespective of the sign of x and y, as long as x > y (leaving the sign), x^2 - y^2 will always be > 0.

As both the statements say that x > y (leaving the sign part), both statements alone are sufficient.

Answer: D
Top
Senior | Next Rank: 100 Posts
Posts: 50
Joined: Tue Oct 13, 2009 1:25 am
Thanked: 14 times
GMAT Score:720

by November Rain » Wed May 12, 2010 10:05 am
Hi,

I agree that statment 1 is sufficient, but i am not sure about 2.

take X = -3 and Y = -4

This means that |x|>y, but, x^2 - y^2 < 0
Top
Master | Next Rank: 500 Posts
Posts: 216
Joined: Mon Dec 21, 2009 10:26 am
Thanked: 16 times

by student22 » Wed May 12, 2010 10:10 am
Can't you just simply square both sides of each statement? That way we don't have to worry about sign changes. Or am I oversimplifying it?
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 66
Joined: Tue Dec 15, 2009 3:07 am
Location: Bangalore
Thanked: 9 times
GMAT Score:730

by ballubalraj » Fri May 14, 2010 2:13 am
I guess November Rain is correct. GMAT always tricks us with simple looking but tricky questions - ineuqalities and modes are probably the best examples.

So the answer should be A.

Any thoughts?
Top
Senior | Next Rank: 100 Posts
Posts: 74
Joined: Fri Oct 09, 2009 4:20 pm
Thanked: 4 times

by nakul_anand » Fri May 14, 2010 2:57 am
Yep...I think that the answer should be A

November Rain's values - -3 and -4 prove that a^2-b^2 can be less than 0.
Top
Master | Next Rank: 500 Posts
Posts: 226
Joined: Sun Aug 09, 2009 4:34 am

by ern5231 » Sun May 16, 2010 12:45 am
Also does not work out when x=2 and y=-1
Top
Post new topic Post Reply
• Page 1 of 1