Check your work using the NORMDIST function or the NORMINV (p 225, Appendix C) and tell what the complete Excel command was in your answer.
Current parameters of process – Changing oil in a car
After studying the process of changing oil, the shop’s manager has found that the distribution of service times, X, is normal with a mean = 28 minutes and a standard deviation = 5 minutes.
Questions:
#1 What proportion of cars will be finished in less than half an hour (30 minutes)?
#2 What is the chance that a randomly selected car will take longer than 40 minutes?
#3 What service time corresponds to the 90th percentile?
#4 The manager wants to be able to service 80 percent of the vehicles within 30 minutes. What must be the mean service time be to accomplish this goal