A pharmaceutical company produces vials filled with morphine (Communications in Statktics, Vol. 27, 1998). Most of the time the filling process remains stable, but once in a while the mean value shifts off the target of 52.00 grams. To monitor the process, one sample of size 3 is drawn from the process every 27 minutes. Measurements for 20 consecutive samples are shown in the table.
a. Construct an 
-chart for these data.
b. What does the -chart suggest about the stability of the process?
c. Is the process influenced by both common and special causes of variation? Explain.
d. Should the control limits and centerline of the chart of part a be used to monitor future output of the morphine filling process? Explain