I'm working on GMAT prep now. Okay, can someone please tell me what the deal is with data sufficiency questions?

A typical question goes like this:

How old is Kay?

1. Kay is fifteen years older than Michael was two years ago

2. Michael is half as old as Kay was two years ago.

A) Statement 1 alone is sufficient but statement 2 alone is not sufficient to answer the question asked.

B) Statement 2 alone is sufficient but statement 1 alone is not sufficient to answer the question asked.

C) Both statements 1 and 2 together are sufficient to answer the question but neither statement is sufficient alone.

D) Each statement alone is sufficient to answer the question.

E) Statements 1 and 2 are not sufficient to answer the question asked and additional data is needed to answer the statements.

This one that I just made up isn't that hard, but there are many where I get stuck. Or, I fall into the trap of choosing B when Statement 2 alone isn't sufficient, but I read Statement 2 with Statement 1 still in the back of my mind, and I wrongly think that Statement 2 is sufficient.

GMAT prep makes my brain melt. Arrrgghhhh!