What is the interquartile range of this set of data? 15, 19, 20, 25, 31, 38, 41

First, you have to find the median, which is the number in the middle: 25

Then cut the data in half by the median, so your new data sets are
15,29,20
    and 
31,38,41

Now you find the median of both of those sets, which is 29 and 38.

The interquartile range is the difference between the numbers, so 38-29 = 9.

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