PSMII is tough because there are 30 questions and a pass of 85%. However, there appears to be partial credit given for some of the questions. Quite a few questions ask you to choose 3 options and you have a high chance of choosing 2 correct ones but 1 wrong one, so I'm glad that there's partial credit. I deduce this from the fact that:
27/30 = 90% and 28/30=93.3%