The National Bank of Warwick is concerned with complaints from customers about its drive-through…

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The National Bank of Warwick is concerned with complaints from customers about its drive-through…

The National Bank of Warwick is concerned with complaints from customers about its drive-through window operation. Customers complain that it sometimes takes too long to be served and since there are often cars in front and back of a customer, they cannot leave if the service is taking a long time. To correct this problem the bank installed an intercom system so the drive-through window teller can call for assistance if the line backs up or a customer has an unusually long transaction. The bank”s objective is an average custome”s waiting and service time of approximately 3 minutes. The bank”s operations manager wants to monitor the new drive-through window system with SPC. The manager has timed five customers” waiting and service times at random for 12 days as follows:

Sample Observation Times (min)
1 2 3 4 5
1 3.05 6.27 1.35 2.56 1.05
2 7.21 1.50 2.66 3.45 3.78
3 3.12 5.11 1.37 5.20 2.65
4 2.96 3.81 4.15 5.01 2.15
5 3.25 3.11 1.63 1.29 3.74
6 2.47 2.98 2.15 1.88 4.95
7 6.05 2.03 3.17 3.18 2.34
8 1.87 2.65 1.98 2.74 3.63
9 3.33 4.15 8.06 2.98 3.05
10 2.61 2.15 3.80 3.05 3.16
11 3.52 5.66 1.18 3.45 2.07
12 3.18 7.73 2.06 1.15 3.11

Develop an -chart to be used in conjunction with an R-chart to monitor this drive-through window process and indicate if the process is in control using these charts.


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