Answer questions 2 - 5 dealing with the life expectancy of light bulbs whose lifetimes are normally distributed with a mean life of 750 hours and with a standard deviation of 80 hours. Show or explain how you determine the appropriate z-score and related percentage.

1. What percent of light bulbs will last longer than 870 hours?
2. What percent of light bulbs will last between 730 hours and 850 hours?
3. What percent of light bulbs will last less than 770 hours?
4. Inverse Normal Distribution: If the quality control program of the company can consistently eliminate the worst 10% of the bulbs manufactured, the manufacturer can safely offer customers a money-back guarantee on all lights that fail before __________ hours of burning time.

(Problems 6 - 10) An investigator polls a representative sample of common cold sufferers, asking them to estimate the number of hours of physical discomfort caused by their most recent cold. Their estimates approximate a normal curve with a mean of 83 hours and a standard deviation of 20 hour.

1. What percentage of sufferers estimate that their colds lasted for longer than forty-eight hours?
2. What percentage suffered for fewer than 61 hours?
3. What percentage suffered for between one and three days?
4. Inverse Normal Distribution: What is the estimated number of hours for the shortest-suffering 10 percent?
5. Inverse Normal Distribution: A medical researcher wishes to concentrate on the 20 percent who suffered the most. She will work only with those who estimate that they suffered for more than _____hours.