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.