Random samples of tires being replaced by a car dealer showed the tire life (miles) below, based on whether or not the owner had checked once a month for recommended tire inflation. Use α = .05 in the following questions.

(a) Are the population variances equal?

(b) Do the population means differ?

(c) What is the advantage of answering (a) before (b)?

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Checked 46,540 36,970 40,430 40,120 42,780 40,330 37,670 46,210 Not Checked 28,260 47,450 44,300 37,870 32,200 33,880 22,650 37,310