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

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:

Solution:

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