Each day 400 inventory control records are cycle-counted for errors. These counts have been made over a period of 20 days and have resulted in the following proportion of records found in error each day:

a. Calculate the center line, upper control limit, and lower control limit for a p control chart. b. Plot the 20 points on the chart and determine which ones are in control. c. Is the process stable enough to begin using these data for quality control purposes?

0.0075 0.0050 0.0025 0.0150 0.0200 0.0125 0.0025 0.0075 0.0050 0.0150 0.0050 0.0150 0.0175 0.0200 0.0075 0.0100 0.0150 0.0125 0.0125 0.0075