The manager of a fleet of automobiles is testing two brands of radial tires and assigns one tire of each brand at random to the two rear wheels of eight cars and runs the cars until the tires wear out. The data (in kilometers) follow. Find a 99% confidence interval on the difference in the mean life. Car Brand 1 Brand 2
1 36663 33866
2 43509 41829
3 36240 35500
4 32100 31950
5 37210 38015
6 48360 47800
7 38200 37810
8 33500 33215
a) Calculate SD =
b) Calculate a 99% two-sided confidence interval on the difference in mean life.
c) Which brand would you prefer? (brand 1/ no difference /brand 2)