After studying the process of changing oil, the shop’s manager has found that the distribution of service times

 – Normal Distribution

Changing oil in a car

Current parameters of process of 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 to answer from the sample information:

1. What proportion of cars will be finished in less than half an hour (30 minutes)?

1. What is the chance that a randomly selected car will take longer than 40 minutes?

1. What service time corresponds to the 90^th percentile?

1. 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

Instructions:

• Use the z – table (Areas under the Normal Curve) to determine the probabilities for #1 – 4. Explain.
• Check your work using the NORMDIST function or the NORMINV and tell what the complete Excel command was in your answer. Explain