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In a data set, the difference between the upper and lower quartiles is called the interquartile range.

For example:

Find the interquartile range:

2, 4, 5, 4, 8, 7, 8, 7, 3, 1

You start by arranging the data set in order from least to greatest:

Now, in order to find the lower quartile and the upper quartile, we need to cut the data in half, like this:

The half is between the red 4 and the red 5.


We need to find the lower quartile which is the mean of the first half set of data:

We have 5 numbers in the first half. The middle number is 3 so the lower quartile in this case is 3

Now we need to find the upper quartile, and as you can see, we have 5 numbers in the second half:

The middle number is 7 so the upper quartile in this case is 7.

Now we have:

Now try:

Find the interquartile range:

26, 36, 34, 25, 40, 41, 27, 32, 35, 38, 42.

Solution:

In Part 6, I will explain how to find the mean of a set of numbers from a table.
Part 1: https://steemit.com/mathematics/@ghostgtr/mathematics-statistics-application-on-cumulative-frequency-part-1
Part 2: https://steemit.com/mathematics/@ghostgtr/mathematics-statistics-application-on-mean-part-2
Part 3: https://steemit.com/mathematics/@ghostgtr/mathematics-statistics-construct-the-relative-frequency-table-of-a-set-of-numbers-part-3
Part 4: https://steemit.com/mathematics/@ghostgtr/mathematics-statistics-how-to-draw-a-histogram-part-4


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