A car servicing shop wants to test the claim that the mean number of sets of wiper blades needed per year is lower for Brand A than for Brand B. A random sample of 35 customers using Brand A needed a mean of 1.2 sets of blades per year, and 30 randomly selected customers using Brand B needed a mean of 1.3 sets of blades per year. Assume that the population standard deviation for Brand A and Brand B are 0.3 and 0.7 set per year, respectively.

a. State the hypotheses

b. Is there sufficient evidence at the 0.15 level to say that the mean number of sets of wiper blades needed per year is lower for Brand A than for
Brand B.

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a Null hyp... View the full answer