Most auto batteries are made by just three manufacturers—Delphi, Exide, and Johnson Controls Industries. Each makes batteries sold under several different brand names. Delphi makes ACDelco and some EverStart (Walmart) models. Exide makes Champion, Exide, Napa, and some EverStart batteries. Johnson Controls makes Diehard (Sears), Duralast (AutoZone), Interstate, Kirkland (Costco), Motorcraft (Ford), and some EverStarts. To determine if who makes the auto batteries affects the average length of life of the battery, the samples in the file titled Start were obtained. The data represent the length of life (months) for batteries of the same specifications for each of the three manufacturers.
a. Determine if the average length of battery life is different among the batteries produced by the three manufacturers. Use a significance level of 0.05.
b. Which manufacturer produces the battery with the longest average length of life? If warranted, conduct the Tukey-Kramer procedure to determine this. Use a significance level of 0.05.