Comparing Scores

My Gmat test date is just a week away. I did the exams on the POWERPREP CD ( from ETS), scored 700, 750. Then I went on to take tests from the Kaplan CD on which I scored 590, 620, 630. Earlier I had taken tests on the Powerprep website, recieved scores of 590, 630, 700.

Evidently, my scores span the whole range from 600-750 and I am worried that I am not constantly able to delived a targetted score(700+).

I would appreciate any tips from previous GMAT test takers (actual test) as to what kind of questions to expect on test day. ie, would the questions be on the level of the ones on: POWERPREP/KAPLAN/PRinceton Review.

Also on the math section, Permutations&Comibations aree the only areas i fear, does any one know if these questions are very likely to appear on the GMAT exam, because i didnt find many on the POWERPREP tests and even in
'The Official Guide for GMAT Review' by ETS.