Hi semwal,

This types of DS questions are perfect for TESTing values and tracking the results.

Here, we're told that zt < -3

There's a Number Property at play here: this means that one of the variables is positive and one is negative. They can't both be negative and they can't both be positive (and neither can be = 0).

The question asks "is z < 4?"

Fact 1 tells us that z < 9
Let's TEST values:
t = -1
z = 8
These values fit all the facts that we have; the answer to the question would be NO

Now, let's keep the t and change the z:
t = -1
z = 3.5
These values fit all the facts that we have; the answer to the question would be YES
Inconsistent answers = INSUFFICIENT

Fact 2 tells us that t < -4
Let's TEST...
t = -5
z = 10
These values fit all the facts that we have; the answer to the question would be NO

Now, let's keep the t and change the z:
t = -5
z = 3
These values fit all the facts that we have; the answer to the question would be YES
Inconsistent answers = INCONSISTENT

Combing Facts, we know that the t is negative (from Fact 2), so the z MUST be positive (from the info in the prompt).
We don't know HOW POSITIVE though. Z could be small (YES answer) or big (NO answer)

Final Answer: E

GMAT assassins aren't born, they're made,
Rich