Oh, it can get pretty hard, like it is for me right about now
I don't mean to scare you at all, but this is how it's been going for me lately:
For my "bugs and drugs" exam two weeks ago (Friday), we had about 52 questions on the exam. Getting a 90% means you can't miss more than 5 questions. After you do an individual assessment, you get the opportunity to take the exam with your "team". I think with the team we could only miss no more than 2 or 3 questions in order to get 3 extra points for the exam. That means if my team passed (and it did), I could miss 8 point out of 52 to pass. I passed this assessment, but only about 35 or 40 out of a class of about 107 passed, the rest had to take a remediation exam on the following Monday. This time, you don't have "team points". I think they had about 52 different questions, which means you can miss no more than 5 questions. The prize for failing the remedial assessment is to repeat that portion of the block (1 week) over the summer. You only have about 6 weeks available...so you can't fail more than 6 remediations in the year...you'll be asked to withdraw from the program if that happens, and this may have been the fate of a number of 1st year students this year.
I've been lucky....I haven't had to remediate an exam (although I have gotten close on a number of occasions). Also, not every exam is as tough as the situation I just cited. This is perhaps the toughest part of the didactic curriculum: infectious diseases, oncology, etc. We have exams where almost everyone passes, and we have our killer exams (like that one). Quite a few of our exams have more test items than the one I just cited...we usually have around 75 questions, so 90% means you could miss around 7 questions on your own, 10 or 11 with your team....more questions help, more room for error.