A shipping firm suspects that the mean life of a certain brand of tire used by its trucks is less than 35,000 miles. To check the claim, the firm randomly selects and tests 18 of these tires and gets a mean lifetime of 34,200 miles with a standard deviation of 1200 miles. At α = 0.05, test the shipping firm's claim. Round the test statistic to the nearest thousandth.


Step 1) Write the null and alternative hypotheses.






Step 2) State a level of significance α. Determine the critical value and critical region.








Step 3) Compute the test statistic. Use classical approach or P-value approach.










Step4) Compare the critical value with test statistic or P-value with α.







Step5) State the conclusion.