Computer upgrades have a nominal time of 30 minutes. Five sets of samples of six observations each have been taken, and the results are listed below. Using the factors in Appendix B, page 417, determine upper and lower control limits for mean and range charts, and decide if the process is in control.
Samples
1 2 3 4 5
20.5 19.3 19.1 18.7 20.2
21.4 18.9 19.5 19.6 19.6
19.8 21.6 20.6 19.8 20.4
20.4 18.6 20.3 19.4 20.8
19.4 19.9 20.6 21.2 18.9
20.9 19.5 21.1 20.1 21.0