Twenty-five samples of 100 items each were inspected when a process was considered to be operating satisfactorily. In the 25 samples, a total of 135 items were found to be defective.
a. What is an estimate of the proportion defective when the process is in control?
b. What is the standard error of the proportion if samples of size 100 will be used for statistical process control?
c. Compute the upper and lower control limits for the control chart.