The formula for the arithmetic mean of a group of numbers is A = S/N, where S represents the sum of all the numbers in the group, and N represents the total number of items in the group. Finding the arithmetic mean is essentially the same as taking the average.
For example, consider the following list of numbers: 72, 88, 68, 91 and 97. The sum of all the numbers on the list is 416, and the number of items in the list is five. Dividing 416 by five gives a quotient of 83.2, which is the arithmetic mean of the numbers on the list.