How can you find the grade average from 20 wrong out of 75 questions?

If you got 20 problems wrong on a 75 question test your grade would be 73% or a C. You can find that by subtracting the amount of questions you got wrong from the amount you got right, 55 in this case. Divide the amount of correct questions by the amount of questions on the test to get .733333. That is the grade.