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

Redeem

Is |x | = y - z ?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 1172
Joined: Wed Apr 28, 2010 6:20 pm
Thanked: 74 times
Followed by:4 members

by uwhusky » Tue Aug 17, 2010 12:09 am
I want to lean toward E...

|x| = y - z could be either -x = y - z or x = y - z.

1) x + y = z confirms one of the two, but not both...insufficient.
2) x < 0 says pretty much the same thing as 1...insufficient.

I don't even know if I am on the right track.
Top
User avatar
Legendary Member
Posts: 1893
Joined: Sun May 30, 2010 11:48 pm
Thanked: 215 times
Followed by:7 members

by kvcpk » Tue Aug 17, 2010 12:13 am
GMAT Hacker wrote:Is |x | = y - z ?

(1) x + y = z

(2) x < 0


I will post QA after some discussion.
(1) x + y = z
x= y-z
put y=2, z=1
x=2-1 = 1
now, |1|=2-1..TRUE
put y=1,z=2
x=1-2 = -1
now|-1| = 1 is not equal to 1-2..FALSE
INSUFF

(2) x < 0
no info about y,z..Hence INSUFF

combining:
x<0
means |x| = -x
so, -x= y-z??

x=y-z
x<0 -> y-z<0
hence y-z cannot equal z-y
-x = z-y is not equal to y-z.. always NO

SUFF

pick C
"Once you start working on something,
don't be afraid of failure and don't abandon it.
People who work sincerely are the happiest."
Chanakya quotes (Indian politician, strategist and writer, 350 BC-275BC)
Top
Senior | Next Rank: 100 Posts
Posts: 51
Joined: Mon Jul 13, 2009 4:25 pm
Thanked: 1 times

by ymach3 » Fri Aug 20, 2010 4:33 am
one more for C
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 78
Joined: Fri Jul 23, 2010 2:22 am
Thanked: 2 times
Followed by:1 members

by gig92 » Fri Aug 20, 2010 5:04 am
GMAT Hacker wrote:Is |x | = y - z ?

(1) x + y = z

(2) x < 0


I will post QA after some discussion.

|X| is always going to be +ve, so the question becomes is y-z > 0 ?

1) x = z - y, does not give any info abt y or z thus INSUFF

2) x < 0 but no idea about y OR z thus INSUFF

1) and 2) together give z - y = -ve thus y-z = +ve (chaging signs on both sides) thus we have an answer
thus

Ans:C
gig92
Top
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Tue Aug 17, 2010 10:55 am
Thanked: 2 times

by wdgolden » Fri Aug 20, 2010 7:09 am
Is |x | = y - z ?
(1) x + y = z
(2) x < 0

Absolute value creates two equations.

x = y-z (if x is positive)
x = z-y (if x is negative)

Statement (1) says
x + y = z or
x = z - y
so if x is negative the original statement is true, but we don't know if x is positive so insuff

Statement (2) gives us no information about y or z so insuff

Together
Statement (2) says x is negative which means we only need to find out if the "x is negative" equation (x = z-y) is correct. Statement (1) says that statement is correct so together they're sufficient.
Top
Master | Next Rank: 500 Posts
Posts: 117
Joined: Wed Jun 09, 2010 7:02 am

by missrochelle » Sun Aug 22, 2010 3:51 pm
This problem really confuses me....

I understand that the absolute value CREATES two equations, but I don't get what the DS question stem is asking us to do with that -- is it to confirm which one is true?

Yes |x| = y-z, if x is positive
or
No |x| does not equal y-z it actually equals z-y, if x is negative.

I'm just having trouble articulating what we are saying "yes/no" to on this D.S. question.
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 44
Joined: Sun Dec 27, 2009 8:50 am
Thanked: 3 times
GMAT Score:710

by skprocks » Sun Aug 22, 2010 7:02 pm
GMAT Hacker wrote:Is |x | = y - z ?

(1) x + y = z

(2) x < 0
I will post QA after some discussion.
Basically we need to check if y-z > 0.From Stmt1: we do not have any info about the nature of x,y and Z.So, I is insufficient.
From Stmt 2: X is negative.This does not indicate anything about y and z.
Combining I and II , x=z-y and x<0 so, z-y < 0 i.e. y-z > 0 (multiplying both sides of inequality by -1)
Hence, IMO : C
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Sun Aug 22, 2010 7:24 pm
Solution:
l x l = x if x >= 0
= -x if x < 0.
So the question is asking that
is x = y - z if x > = 0?
Or is -x = y - z if x < 0?

First consider statement (1) alone.
It says x + y = z.
Or - x = y - z.
But we know nothing about x whether it is greater than or less than zero.
Or (1) alone is not sufficient.

Next consider just statement (2) alone.
x < 0.
But we know nothing about y and z.
So obviously statement (2) alone is not sufficient

Next combine both the statements and check.
On combining we have that - x = y - z and x < 0.
Since l x l = -x if x < 0.
We have l x l = y - z

So both statements together are sufficient.
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Post new topic Post Reply
• Page 1 of 1