You have to remember, teachers like to do exams differently. Image an exam that is designed for two hours. Take it in 50 minutes. Image a teacher who likes to design every single problem to be difficult and tricky, so you will fail. I think the high for anyone was 51%.
The reason I got a 35% was because I did about half the problems, and most of them were right. I knew the material, but the teacher like to grade like this, and made it clear in the beginning. A friend of mine had a Physics professor where it was impossible to have a higher grade than your first day. Why? Because he didn't like grades, so instead he took off points. You did a problem but wrong answer? Eh, -5. Didn't hand in lab report? Lets make that -50 this time. Did a problem the wrong way, in such a way that he warned you not to do it in lecture? -5,000. He'd rather you not do a problem than to fake it.
I believe he gave the final grades by just ranking everyone and drawing lines saying this group gets A's, B's, etc.