- Consider the problem of determining whether or not different brands of tiers exhibit different amount of tread loss after 20,000 miles of driving. A fleet manager wishes to consider four brands A, B, C, and D that are available and make some decision about which brand might show the least amount of tread wear after 20,000 miles. The variable to be measured (i.e Response variable or study variable) is the difference in maximum tread thickness on a tire between the time it is mounted on the wheel of a car and after it has completed 20,000 miles on this car. Because of the performance of the cars four cars were used and each car got one tire of each brand and the following data about difference in thickness in mils(0.001 inch) were recorded Car I II III IV B (14) D (11) A (13) C (9) C (12) C (12) B (13) D (9) A (17) B (14) D (11) B (8) D (13) A (14) C (10) A (13) (a):- Test the hypothesis that the performance of four brands of tires are same. (b):-Calculate C.V and interpret it.