Final answer:
The median of the data set 3, 3, 3, 5, 7, 9, 12 is 5, as it is the middle value of the ordered data set with an odd number of values.
Step-by-step explanation:
To find the median of the data set 3, 3, 3, 5, 7, 9, 12, we must first arrange the data in numerical order, which has already been done. Since there are seven numbers in the data set, which is an odd number, the median is the middle value. In this case, there are three numbers on either side of the middle value, so the median is 5.