Group A consists of the five values 3, 7, 9, 15, 21 and Group B of the four values 5, 11, 13, 25. The two groups are put together to form one set of nine values. What is the median of the combined set?

Merge and order the nine values: 3, 5, 7, 9, 11, 13, 15, 21, 25. With nine observations the median is the 5th value, which is 11. Note that a combined median is NOT the average of the two group medians — those are 9 and 12, whose average 10.5 is not the answer. Medians cannot be pooled the way totals can.