The McGranger Mortgage Company is interested in monitoring the performance of the mortgage process. Fifteen samples of five completed mortgage transactions each were taken during a period when the process was believed to be in control. The times to complete the transactions were measured. The means and ranges of the mortgage process transaction times, measured in days, are as follows:Subsequently, samples of size 5 were taken from the process every week for the next 10 weeks. The times were measured and the following results obtained:

a. Construct the control charts for the mean and the range, using the original 15 samples.
b. On the control charts developed in part (a), plot the values from samples 16 through 25 and comment on whether the process is in control.

c. In part (b), if you concluded that the process was out of control, would you attribute it to a drift in the mean, an increase in the variability, or both? Explain your answer.

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Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Mean 17 14 8 17 12 13 15 16 13 14 16 9 11 9 12 8 9 14 12 15 10 10 11 6 9 11 13 Range 6 11 4