The mean (or average) of a series of numbers of length n is defined as the sum of the numbers in the series divided by n. In formula form this is shown as follows:

\( AV = \frac{1}{n} \sum_{i=1}^{n} a_i = \frac{1}{n}(a_1+a_2+a_3+\cdots+a_n) \)

For example: if our series of numbers is 1 2 3 4 5, then the mean is equal to \( \frac{1}{5} \times (1+2+3+4+5) = \frac{1}{5} \times 15 = 3 \).