The manager of a branch of a local bank has the business objective of reducing the waiting times of customers for teller service during the 12:00 noon-to-1:00 p.m. lunch hour. A subgroup of four customers is selected (one at each 15-minute interval during the hour), and the time, in minutes, is measured from when each customer enters the line to when he or she reaches the teller window. The results over a four-week period, stored in BankTime, are as follows:
Day |
| Time (Minutes) |
| |
1 | 7.2 | 8.4 | 7.9 | 4.9 |
2 | 5.6 | 8.7 | 3.3 | 4.2 |
3 | 5.5 | 7.3 | 3.2 | 6.0 |
4 | 4.4 | 8.0 | 5.4 | 7.4 |
5 | 9.7 | 4.6 | 4.8 | 5.8 |
6 | 8.3 | 8.9 | 9.1 | 6.2 |
7 | 4.7 | 6.6 | 5.3 | 5.8 |
8 | 8.8 | 5.5 | 8.4 | 6.9 |
9 | 5.7 | 4.7 | 4.1 | 4.6 |
10 | 3.7 | 4.0 | 3.0 | 5.2 |
11 | 2.6 | 3.9 | 5.2 | 4.8 |
12 | 4.6 | 2.7 | 6.3 | 3.4 |
13 | 4.9 | 6.2 | 7.8 | 8.7 |
15 | 7.1 | 5.8 | 6.9 | 7.0 |
16 | 6.7 | 6.9 | 7.0 | 9.4 |
17 | 5.5 | 6.3 | 3.2 | 4.9 |
18 | 4.9 | 5.1 | 3.2 | 7.6 |
19 | 7.2 | 8.0 | 4.1 | 5.9 |
20 | 6.1 | 3.4 | 7.2 | 5.9 |
a. Construct control charts for the range and the mean.
b. Is the process in control?
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