Test Hypotheses About a Population Mean with Unknown
-A Shipping $\alpha = 0.05$

Test Hypotheses about a Population Mean with Unknown
-A shipping firm suspects that the mean life of a certain brand of tire used by its trucks is less than 36,000 miles. To check the claim, the firm randomly selects and tests 18 of these tires and gets a mean lifetime of 35,350 miles with a standard deviation of 1200 miles. At $\alpha = 0.05$ , test the shipping firm's claim.