To calculate the overall percentage, you need to sum up the marks obtained by the students in all subjects. Divide the product by the sum total of marks of all subjects. Then, multiply the answer with 100.
For example, if a student obtained 80, 60, 70, 87, and 85 in 5 subjects. All the exam conducted was 100 marks each. Thus, to find the percentage do as following:
80 + 60 + 70 + 87 + 85 = 382
Sum total of marks 5 X 100 = 500
Percentage = (385/500) X 100 = 76.40 %
For a single subject, same formula will apply.
= (87/100) X 100 = 87 %.