Gmat prep not happy with OA !

[mazwaz]

is m + z > 0 ?

(1) m - 3z > 0
(2) 4z - m > 0

Clearly each statement alone is not sufficient!!!
and together we get : 3z < m < 4z
so if z = -2 then m + z < 0
if z = 2 then m + z > 0

I don't understand how it can't be OA E ???

[Brent@GMATPrepNow]

is m + z > 0 ?

(1) m - 3z > 0
(2) 4z - m > 0

Clearly each statement alone is not sufficient!!!
and together we get : 3z < m < 4z
so if z = -2 then m + z < 0
if z = 2 then m + z > 0

I don't understand how it can't be OA E ???

This is a tricky question.
Let's start with your (very correct) conclusion that 3z < m < 4z
Notice that we can use this to conclude that 3z < 4z
From here, if we subtract 3z from both sides, we get 0 < z
In other words, z is positive.
If z is positive, then 3z is positive, and since 3z < m, we know that m is positive.

If z and m are both positive, then m+x > 0, so the answer is C.

Aside: notice that z cannot equal -2 (as you suggested) since that would contradict the fact that 3z < 4z

Cheers,
Brent

[mazwaz]

ohh yeah I didn't see that!!
Now it is clear!
Thanks for your quick reply!!!

[HSPA]

Add the two statements: m-3z+4z-m >0 => z > 0

Now using m-3z>0 => m > 3Z => m is +ve, z is positive

thus m+z is +ve... IMO C

[force5]

z>0 gives C