the MGMAT book
has EVERYTHING you need to know. My advice is go back through the topics. There is no other book on the market that is better prepared to teach you GMAT statistics.
Also, don't spend TOO much time on GMAT propability. You will most likely not see more than a few of these questions on test day. And you will only get them if you are doing well on the quant. So your time may be better spent in other areas of study, unless you are shooting for a Q48 or above. Then you should definitely review the book again.
. But if i compare the probability sections with some questions posted here, i can't hardly solve them while the MGMAT exercises aren't really a hard problem.