Referring to Problem 18-14, if necessary delete any out-of-control points and construct the appropriate x - 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:

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 x -chart. Is there evidence to suggest that the process has gone out of control with respect to the process mean? Discuss.

33 34 35 363738 Subgroup Subgroup Mean89.0 88.4 85.2 89.3 97.2 05.3 Subgroup Ran 5.4 4.2 1.79.5 10.2