Suppose that you are interested in comparing the gasoline mileage of two brands of gasoline. You hypothesize that there is no difference in the mileages, and you assume that the mileage for each brand is normally distributed with unknown variance cr2. A sample is taken from each brand, with the following results:

Brand A Brand B 16 13 18 15 15 11 23 17 17 12 14 13 19 21 16