Hi,

I found the following problem in the Gmatprep test:

Is y < (x+z)/2?

1) y - x < z - y
2) z - y > (z- x)/2

OA is D.


I tried the following way:
1. y - x < z - y => 2y < Z +x => y < (z+x)/2 - SUFFICIENT

2. z - y > (z -x)/2 => 2z - 2y > z -x => z + x > 2y
=> (z+x)/2 > y - SUFFICIENT

So, the answer should be D.

BUT ... the above rationale is correct only if x,y,z are positive, so the signs of the inequalities do not change.
Please help, thanks.