Referring to Exercise 18-23, if necessary delete any out-of-control points and construct the appropriate -

and R-charts. Now, suppose the process stays in control for the next six weeks (subgroups 18 through 23). The subgroup means and ranges for subgroups 33 to 38 are as follows:

Subgroup 33 34 35 36 37 38 Subgroup Mean 89.0 88.4 85.2 89.3 97.2 105.3 Subgroup Range 11.4 5.4 14.2 11.7 9.5 10.2

a. Plot the ranges on the R-chart. Is there evidence based on the range chart that the process has gone out of control? Discuss.

b. Plot the subgroup means on the -chart. Is there evidence to suggest that the process has gone out of control with respect to the process mean? Discuss.