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 bankâ€s objective is an average customeâ€s waiting and service time of approximately 3 minutes. The bankâ€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.