The quality control manager at a light bulb factory needs to determine whether the average life of a large shipment of light bulbs is equal to the specified value of 475 hours. The process standard deviation is known to be 100 hours. A random sample of 25 light bulbs indicates a sample mean life of 480 hours. At the 0.10 level of significance, is there evidence that the mean life is different from 475 hours? [10 points]

a. State the null and alternative hypothesis

b. Is it a two-tail test or one-tail test?

c. Write the test Statistic (Z or T)?

d. State the critical value(s)

e. State the conclusion (Reject Ho or Do not reject Ho)

f. State the conclusion as a relationship to the problem.