The short answer is that you don't really know. A perfect score on a CLEP is an 80, and if you manage to answer every question wrong, you get a 20. A 50 is the mean raw score of everybody who took the exam during the evaluation, but you don't know what that raw score is. Not only that, but some of the questions you will answer will not count toward your score, but are being evaluated for future versions of the exam -- and you will not know which questions those are.

But having said all that, a 71% raw score on a Peterson's exam probably means you are ready to pass the real exam. I never took any Peterson's exams, so take what I say with a grain of salt, but if I were scoring in the 70s on an Official Guide practice exam, I'd feel like I was ready for the real thing.

-Gary-