10/13 right = 77% grade
84.6 around that
That is about a "C".
As a percentage it is 80%
You use division. For example 13/47 is approximately 0.276 or 28%. 100-28 is 72 so the grade would be a 72.
10/13 right = 77% grade
77% or C+
12/13 correct is a 92% which is an A-
54% or F
84.6 around that
8/13 right = 62 %
That is about a "C".
13 wrong out of 85 is 72 correct. So percentage score = 100*72/85 = 84.7%
As a percentage it is 80%
88%, or a B+
If by grade you mean percentage, you would have scored 67.5%. 40-13= 27 (27/40) * 100
13 - 4 = 9 correct 9/13 x 100 = 69% (rounded)