Find the number of students if the average score is 8 and the sum of all the scores is 72.
Three Science classes: A, B, and C, take a test
1. The average score in class A is 83
2. The average score in class B is 76
3. The average score in class C is 85
4. The average score of all students in classes A and B together is 79
5. The average score of all students in classes B and C together is 81
What is the average for all three classes?