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Divide the set of data into two groups (high and low) of equal size at the statistical median if there is an even number of data points, or two groups consisting of points on either side of the statistical median itself plus the statistical median if there is an odd number of data points. Find the statistical medians of the low and high groups, denoting these first and third quartiles by Q_1 and Q_3. The interquartile range is then defined by:

IQR congruent Q_3 - Q_1 .

The answer according to the above instructions =5.625. Consult your Stats textbook.

Guest Mar 17, 2017