Average equals the sum of a set of numbers divided by the count which is the number of the values being added. For example, say you want the average of 13, 54, 88, 27 and 104. Find the sum of the numbers: 13 + 54 + 88+ 27 + 104 = 286. There are five numbers in our data set, so divide 286 by 5 to get 57.2.