shocker, we have two types of exams.
First are qualification exams, which gage you're level of knowledge about a particular watchstation. It's not always realistic to expect 100% passing on these. Partly because the exams sometimes ask things that may not be important during day to day ops or even most casualties, but might come up once in a while, plus some people are rocks or poor test takers. Also people sometimes misread the question and give a great answer to the wrong question.
Second are countinuous training exams, which typically come from training you've had over the last month or two and weak areas from previous exams. Personally, I see no reason why there's not a pass rate of at least 90% on these (again, rocks and poor test takers), assuming the questions were covered in training. This is actually something that my last ship was working toward, and, as can be expected, the test scores started going up. All we would get is the topics covered and recently failed areas to study.
Yes, some people do cheat on both of these, most fall into a grey area by asking the proctor to rephrase the question (who then might rephrase in the form af an answer). I've personally asked which version of the question it was, since I'd seen the same question three times with three different answers (and given all three answers). As it turns out, if that happens you're supposed to write several pages for a 4 point question, since the proctor shouldn't answer that, there was an AIRPAC monitor for this particular test.
Then you have the ORSE/MTT exams which come from all the questions on the CTEs from the last six months. Sure, it's possible to cheat, but you're likely to be caught during the oral interviews.