If you have a data set, you can be asked to provide 4 measurements on this data. These are: Lower Quartile (Q1), Median (Q2), Upper Quartile (Q3) and Interquartile Range. The data set must be ordered before working out the 4 measurements.

Suppose our ordered data set is represented by this horizontal line…. the 4 measures are as follows:

So how do you find Q1, Q2 and Q3 ? Examples below

Direct & Inverse Proportions
Negative Numbers - Adding & Subtracting