A course has 2 sections, Section A and Section B. On the last exam, Section A's 10 students had an average score of 80, and Section B's 20 students had an average score of 90. What is the course average score on that exam?
You can't just take the mean. It has to a weighed mean.
First back to basics:
Total score for
The average score:
The other way is to realise that
So we weigh the average for section
Just pick the method that works for you.