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GMAT Prep Question help needed : Tomo is my exam

Expert replies
Source: — Problem Solving |

by kevincanspain » Wed Jun 01, 2011 3:56 am
Is |x| = y - z ?

(1) x + y = z

This tells us that y - z = - x

We know that |x| = x if x > 0 and |x| = - x if x < 0
Thus |x| = y - z if and only if x is less than or equal to 0
However, we don't know the sign of x. NOT SUFF

(2) NOT SUFF
(T) SUFF
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by Frankenstein » Wed Jun 01, 2011 3:59 am
Hi,

From(1): x=z-y. So, |x| = |z-y| = z-y, if x>=0 and y-z if x<=0
Insufficient
From(2): x<0, we know nothing about the relation between x,y,z
Insufficient
Combining (1) & (2)
|x| = y-z
Sufficient

Hence, C
Last edited by Frankenstein on Wed Jun 01, 2011 4:09 am, edited 1 time in total.
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by cans » Wed Jun 01, 2011 4:03 am
|x|=y-z?
a)x+y=z => y-z=-x = |x| only when x<0
insufficient
b)x<0
nothing about y and z. insufficient.
a&b) x<0 thus l.h.s. = -x = y-z
true
IMO C
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