What is the upper and lower quartile of this set of data? 15, 19, 20, 25, 31, 38, 41

The data are already in order, and the middle value is 25. Excluding that median, the lower half is 15, 19, 20, whose middle value is 19; the upper half is 31, 38, 41, whose middle value is 38. Therefore, the lower quartile is 19 and the upper quartile is 38, matching choice C.

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