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

The data are already in order, and the median is 25. Excluding the median, the lower half is 15, 19, 20, so Q1 = 19; the upper half is 31, 38, 41, so Q3 = 38. The interquartile range is Q3 − Q1 = 38 − 19 = 19, which is choice B.

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