What is an 81% grade on an exam?
81% would fall in the B category which is a very good score. When your grade falls between 80 to 89 it is considered as a B. you can go to http://www.altiusdirectory.com/Society/us-education-grade-system.php for more information. I hope that helps.
I'm hoping it's a C.
B- unless there is one of those curves on the grade scale like 95-100 A85-95 B75-85 CWitch in your case may bring a C and confirm your teacher is a d**K