Calculate your course grade from weighted categories.
A course grade is a weighted mean, not an average of averages. Each category average is multiplied by its weight, the products are summed, and the result is divided by the total weight entered rather than by 100 — which means a partially specified syllabus still gives the right answer for the work counted so far. The weight-accounted line is the check on your inputs: if it does not read 100 you have either omitted a category or the weights do not sum as the syllabus intends.
Weighted mean
Grade = sum of (category average x category weight) / sum of weights
Category contribution
Points from a category = category average x its weight / total weight
Because weights differ. An 88 in homework worth 25 percent and a 74 in exams worth 50 do not average to 81 — the exams count twice as much, and the weighted result is 81.75 only by coincidence of these numbers.
The calculation normalises by whatever total you enter, so the grade is correct for the categories included. Check the weight-accounted figure against the syllabus before trusting the result as a final grade.