Students in a business statistics course performed an experiment to test the strength of four brands of trash bags. One-pound weights were placed into a bag, one at a time, until the bag broke. A total of 40 bags were used (10 for each brand). The file Trash bags gives the weight (in pounds) required to break the trash bags.
a. At the 0.05 level of significance, is there evidence of a difference in the median strength of the four brands of trash bags?
b. Compare the results in (a) to those in Problem 11.8 (a) on page 401.