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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.


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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?



9.15   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.