The average of a set of numbers
is the sum of the given numbers of the set divided by the number
of items in the set. Average is also called the arithmetic mean.

Example :

The average of 1, 4, 5 and 6 is 4.

1 + 4 + 5 + 6 = 16

If we divide 16 by the number of items 4, we get average
= 4