To find the mean (average), we first need to add up all the test scores (14 + 19 + 19 + 20 + 16 + 18 + 15 + 17 + 12 = 150). Then, we need to divide that number (150) by the number of numbers in the data set (9 in this case). So the mean of these test scores is about 16.6666666667.
