In this section we will look at three different types of 'average'. These are the mean, the median and the mode.
They are used by statisticians as a way of summarising where the 'centre' of the data is.
The Mean
To calculate the mean, we need to add all the values up and divide by the number of values.
In this case the mean is 9 which is one of the values in the list.= = 9
Sometimes the mean will not appear in the original list. It might even be a decimal value.
The Median
To calculate the median, we need to put the numbers in order and find the middle value.
Here the median is 7 because this is the middle value.3 4 5 5 5 7 9 12 14 16 19
Half of the other values in the list are below 7 and half are above 7.
The Mode
To calculate the mode, we need to look at which value appears the most often. It can help if the numbers are in order.
In this list the mode is 5, because it appears most often.3 4 5 5 5 7 9 12 14 16 19
Sometimes there will be more than one mode, because two or more values appear the same number of times.
For the list: "5, 9, 12, 4, 5, 14, 19, 16, 3, 5, 7", the mean is 9, the median is 7 and the mode is 5.
For example, what is the median of: 3, 6, 7, 8, 11, 15?
In this case, there are two middle values.
The median is the mean of these two middle numbers.
3 6 7 8 11 15
=7.5  
9  8  5  9  12  8  7  6  5  9 
(a) What is the mean of the values above?  
(b) What is the median of the values above?  
(c) What is the mode of the values above? 
