Recall from Problem 18-11 that Tony Perez is the manager of one of the largest chains of service stores that specialize in oil and lubrication of automobiles, Fastlube, Inc. One of the company’s stated goals is to provide a lube and oil change for anyone’s automobile in 15 minutes. Tony has thought for some time now that there is a growing disparity among his workers in the time it takes to lube and change the oil of an automobile. To monitor this aspect of Fastlube, Tony has selected a sample of 24 days and has recorded the time it took to service 100 automobiles each day. The number of times the service was performed in 15 minutes or less (≤ 15) is given in the file Lubeoil.
a. (1) Convert the sample data to proportions and plot the data as a line graph. (2) Compute p and plot this value on the line graph. (3) Compute  and interpret what it measures.
b. Construct a p -chart and determine if the process of the time required for oil and lube jobs is in control.
c. Specify the signals that are used to indicate an out-of-control situation on a p -chart.