i dunno about an actual 10%, but i'd agree with souljah in that if you do about 60%, you should pass... if you get around 70%, you'll do well....
that said, i averaged around 65% overall but got a score in the 250s (not said to sound egotistic or anything)...
what i think is important to realize about kaplan (at least what I think about kaplan) is that much of their questions don't seem to be "test what you know" type questions, per se, but more like "we want to make an educational point here" questions - so if you're not rolling in the 70s, then don't work yourself up too much... just make sure y'all read the explanations on (at least) any questions you're not slam-dunk sure about...
good luck,
-tim