Data Sufficiency

M7MBA wrote:If xy > 0, is xyz < 0?

(1) xz > 0
(2) yz > 0

Since xy>0, x and y have the SAME SIGN.
Statement 1 implies that x and z have the same sign.
Statement 2 implies that y and z have the same sign.
Implication:
When the two statements are combined, all three variables -- x, y and z -- must have the same sign.

Statements combined:
Case 1: x=y=z=1
In this case, xyz = 1, so the answer to the question stem is NO.
Case 2: x=y=z=-1
In this case, xyz = -1, so the answer to the question stem is YES.
Since the answer is NO in Case 1 but YES in Case 2, the two statements combined are INSUFFICIENT.

The correct answer is E.