The Ajax Taxi company in Manhattan, New York, wishes to set up an -chart and an R -chart to monitor the number of miles driven per day by its taxi drivers. Each week, the scheduler selects four taxis and (without the drivers’ knowledge) monitors the number of miles driven. He has done this for the past 40 weeks. The data are in the file Ajax.

a. Construct the R -chart for these 40 subgroups.

b. Construct the x̅-chart for these 40 subgroups. Be sure to label the chart correctly.

c. Look at both control charts and determine if any of the control chart signals are present to indicate that the process is not in control. Explain the implications of what you have found for the Ajax Taxi Company.