Wilson, Ryan, and Reed is a large certified public accounting (CPA) firm in Charleston, South Carolina. It has been monitoring the accuracy of its employees and wishes to get the number of accounts with errors under statistical control. It has sampled 100 accounts for each of the last 30 days and has examined them for errors. The data are presented in the file Accounts.
a. Construct the relevant control chart for the account process.
b. What does the chart indicate about the statistical stability of the process? Give reasons for your answers.
c. Suppose that for the next 3 days, sample sizes of 100 accounts are examined with the following results:

Plot the appropriate data on the control chart and indicate whether any of the control chart signals are present. Discuss your results.