The mean is the average of a set of numbers. Mean = sum / the number of things. On the ACT, however, it’s often more helpful to use this form: sum = mean × things. Questions will often give you the average and ask you to find the sum.
Example: What is the mean of Tony’s exam scores if he scored a 88, 93, 80, and 99 on his exams? Answer: Mean = (88 + 93 + 80 + 99) / 4 = 90.