A trucking firm suspects that the mean life of a certain tire it uses is less than the advertised 45,000 miles. To check the claim, the firm randomly selects and tests 22 of these tires and gets a sample mean lifetime of 44,350 miles with standard deviation of 1200 miles. a) The sample mean is 44,350. Before doing any work, what is gut feeling about the chances of the population mean being less than or equal to 45,000? Do you think that the sample mean of 44,350 is low enough and provides enough evidence? b) Which will you use to perform the hypothesis test, a z-test or t-test? Explain why. c) At α = 0.01, test the advertisement’s claim. d) Complete the hypothesis test and compare with your guess in part a.
A trucking firm suspects that the
a) The sample mean is 44,350. Before doing any work, what is gut feeling about the chances of the population mean being less than or equal to 45,000? Do you think that the sample mean of 44,350 is low enough and provides enough evidence?
b) Which will you use to perform the hypothesis test, a z-test or t-test? Explain why.
c) At α = 0.01, test the advertisement’s claim.
d) Complete the hypothesis test and compare with your guess in part a.
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