Seriously?

So I'm taking an online math class. Everything is online, the textbook, the homework, the quizzes, everything. Well this afternoon I log in and sit to read the chapter for the week and do all the exercises and practice quizzes.
Now for those of you who don't know me I am a perfectionist. Even if I'm not being graded on an assignment I work at it until I get every answer correct. So today was no different. So after you read everything and do all the homework then you take a quiz that shows that you know the material. I got 100 on all the assignments that went with this section so I'm not worried about the quiz.

I take the quiz and get an 83.3%.

Seriously how does that happen. 6 hours of work and 100s on all the assignments that don't count towards our grade and the one that does I get an 83. Don't get me wrong I know 83 is still alright but seriously that is a little frustrating.