Which data set has an outlier?

For set C, the lower quartile is about 18 and the upper quartile is 26, so the interquartile range is about 8. The upper outlier cutoff is Q3 + 1.5 × IQR = 26 + 12 = 38; since 39 is above 38, it is an outlier. Thus, the data set 8, 17, 18, 20, 20, 21, 23, 26, 31, 39 has an outlier.

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