The TV series "2.5 Children" is intended to represent Mr and Mrs Average and their family. Some time ago when statisticians were looking at the numbers of children in families in the UK they announced that the average number of children per family is 2.5!

Mathematically speaking, this number is quite correct, though when applied to children it conjures up images of most of the families in the country being victims of a chain saw massacre.

This number 2.5 was calculated by adding up the number of children in the country and dividing by the number of families.

In creating statistics there are three types of averages which are used (note that the mathemtical word mean is the same as what we commonly call the average):

Mean
This is calculated using the same technique as mentioned for the 2.5 children.

e.g. to find the mean of 1,2,3,4,5,6,7,8,9,10

Add all the values 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10
Note the number of values = 10

Mean = 55 / 10 = 5.5

Median
The median of a set of numbers is the middle number when the numbers are put in order from the lowest value to the highest value.

e.g. to find the median of 4, 6, 3, 8, 7, 3, 6, 1, 2

First put the values in order: 1, 2, 3, 3, 4, 6, 6, 7, 8
The middle value as can be seen is 4 (this is the median)

The median can also be calculated with the formula

Median = (Number of values + 1) / 2.

Using the formula we get (9 + 1) / 2 = 10/2 = 5th value (which again gives us 4 as the median)

Mode
The mode is the value which appears most frequently in a set of values

e.g. the mode of 1, 2, 4, 5, 4, 4, 3, 6, 4, 4,

is obviously 4 as there are more 4's than any of the other values.