Suppose we have the following information from a simple regression

– 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)?

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

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