Question: : Four samples of 3 observations have been taken, with actual measurements (in centimeters). Construct 3 sigma mean range charts, and determine if corrective action is needed.

sample

1 2 3 4

12.3 11.9 12.0 12.1

12.2 12.2 12.2 11.8

12.1 12.2 11.8 11.8