Calculating the mean of a set of numbers is actually too easy. Just take your set of numbers and add them all together. After you’ve done that, divide the amount of numbers that were in the set of numbers by the number you came up with when you added them together. For example, I have 9, 2, and 4. Those added together would be 16. I have 3 numbers in my set, so 3 divided by 15 is 5, and that would be the mean.