Question: Four samples of three observations each have been taken, with actual measurements (in centimeters) shown below. Construct 3 sigma mean and 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