A company that produces industrial food processors guarantees that a unit will be replaced free of charge if it fails within 14,000 hours of its first operation. The average number of hours of operation before failure for these units is 16,000 hours with a standard deviation of 1,200 hours. Assume the distribution of hours before failure is approximately normal. a. What percentage of units will have to be replaced free of charge?
b. What percentage of units operate between 14,500 and 17,000 hours before failing?
c. Suppose the company wants to limit the number of replaced units to 1%. What must the average hours of operation before failure be to achieve that goal?