Testing tires. Goodstone Tire & Rubber Company is interested in monitoring the proportion of defective tires generated by the production process at its Akron, Ohio, production plant. The company's chief engineer believes that the proportion is about 7%. Because the tires are destroyed during the testing process, the company would like to keep the number of tires tested to a minimum. The chief engineer recommended that the company randomly
sample and test 120 tires from each day's production. To date, 20 samples have been taken. The data are presented in the table.
a. Construct a p-chart for the tire production process.
b. What does the chart indicate about the stability of the process? Explain.
c. Is it appropriate to use the control limits to monitor future process output? Explain
d. Is the p-chart you constructed in part b capable of signaling hour-to-hour changes in p? Explain.