The makers of compact fluorescent light bulbs (CFL) claim the bulbs use 75% less energy and last 10 times longer than incandescent bulbs. A 16-watt CFL (equivalent to a 60-watt incandescent) has a rated lifetime of 8,000 hours. To test this claim, a random sample of 50 CFLs was drawn, and the average life of a bulb was determined to be 7,960 hours.

Assume the standard deviation for the life of CFL bulbs is 240 hours.

a. Does this sample provide enough evidence to support the claim that CFLs average 8,000 hours with 95%

confidence?

b. What is the margin of error for this sample using a 95%

confidence interval?

c. Verify your result using Excel.

AppendixLO1