There are a LOT of probability and stats sums in the GMAT PS section in TM. Visit that everytime you log in to TM.
Work on the PP math review for some stats sums. Its a good indicator for stats.
if you have time on your hands, become a member at number2.com and work on their tutorials. its a good service.
i dont have many links for math, most of them are for verbal.check our yahoo mailbox, i saw some Quants files there that may help you.
good luck

and work on your speed. you should be fast.
