For example, if you want to average 10, 20, and 27, first add them together to get 10+20+27= 57. Then divide by 3 because we have three values, and we get an arithmetic mean (average) of 19.

Want a formal, mathematical expression of the arithmetic mean?

That's just a fancy way to say "the sum of k different numbers divided by k."

Check out a few examples of the arithmetic mean to make sure you understand:

Example:

Find the arithmetic mean (average) of the following numbers: 9, 3, 7, 3, 8, 10, and 2.

Solution:

Add up all the numbers. Then divide by 7 because there are 7 different numbers.

Example:

Find the arithmetic mean of -4, 3, 18, 0, 0, and -10.

Solution:

Sum the numbers. Divide by 6 because there are 6 numbers.

The answer is 7/6, or 1.167