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

7490

hours. The population standard deviation is

840hours.

A random sample of

64

light bulbs indicates a sample mean life of

7,259

hours.

a. At the

0.05

level of significance, is there evidence that the mean life is different from 7490hours?

b. Compute the p-value and interpret its meaning.

c. Construct a

95%

confidence interval estimate of the population mean life of the light bulbs.

d. Compare the results of (a) and (c). What conclusions do you reach?

e. Compare the results of parts (a) through (d) to those when the standard deviation is

1,200

hours.