OK, first post but (as all say) I have been reading for a while and it has been a valuable resource. Well, also slightly intimidating, as everyone seems to have committed a lot more prep time to the GMAT than I could manage.
Anyway, I have the test tomorrow, and on the practice test only got one question that I cannot resolve. It was the first one, I got it wrong, and I can't work out the underlying process to get the answer (all the others made fair sense).
5^21 * 4^11 = 2 * 10^n
Find n. The answers available don't really matter, I would just really appreciate a full solution so I can see what rules I am missing.