Suppose that in Problem 9.14, the standard deviation is 1,200 hours. a. Repeat (a) through (d) of Problem 9.14, assuming a standard deviation of 1,200 hours. b. Compare the results of (a) to those of Problem 9.14. The quality-control manager at a compact fluorescent light bulb (CFL) factory needs to determine whether the mean life of a large shipment of CFLs is equal to 7,500 hours. The population standard deviation is 1,000 hours. A random sample of 64 CFLs indicates a sample mean life of 7,250 hours. a. At the 0.05 level of significance, is there evidence that the mean life is different from 7,500 hours? b. Compute the p-value and interpret its meaning. c. Construct a 95% confidence interval estimate of the population mean life of the CFLs. d. Compare the results of (a) and (c). What conclusions do you reach?