Arithmetic mean
Arithmetic Mean
The arithmetic mean of a set of numbers (or variables) is the sum of all the numbers, divided by the number of numbers. If we let denote Arithmetic Mean,

is the arithmetic mean of thenumbers
.
For example, if I wanted to find the average of the numbers 3, 1, 4, 1, and 5, I would compute:

Arithmetic means are also called averages. Arithmetic means show up frequently in contest problems.