Find the mean:

31, 1, 12, 2, 21, 22, 1, 0, 31, 13

The mean is 13.4 because after I add the numbers in the set, the sum comes out to be 134. There are 10 numbers in the set, so you divide 134 by 10, which is 13.4 (134 : 10 = 13.4). That is how you get the mean. It's "mean" to you because you 'gotta do a lot of work to get your final mean.