Add up all the numbers you have, then divide the total by the number of numbers you added up. For instance...
I want to find the average of 45, 32, and 27.
First, I add up all the numbers. (the total is 104)
Now, I divide this total by the number of numbers I added up. (I added three numbers)
I divide 104 by 3, and I get thirty-four and two-thirds as my average.