The arithmetic mean formula is also sometimes just called the mean. One can arrive at the solution to this formula by adding together all the number in a set and dividing them by the number of items in the set. Essentially one can also look at the mean of a set of numbers as the average of that set of numbers.
The mean serves to show what the median number is for all the numbers that will be listed in a set. This is one of the simpler mathematical operations that one can perform. An example of arithmetic mean in action would be 1+2+3=6/3=2. The arithmetic mean of the number set including 1,2, and 3 is 2.