Spencer’s Food Mart (Spencer, OK) monitors its customers’ checkout times using mean and range charts. Eight samples of n = 20 checkout time observations (in minutes) were collected, and the following sample means and corresponding sample ranges were calculated:

Sample means: 4.06, 5.1, 3.75, 6.3, 5.8, 4.7, 3.9, and 5.0.

Sample ranges: 0.7, 1.0, 0.5, 1.3, 0.9, 0.6, 0.4, and 0.9.

1. Construct a mean chart and a range chart for the checkout time process using 3σ control limits.

2. The following sample means and sample ranges were observed on a particular day:

Sample means: 4.1, 6.0, 4.25, 5.7, 4.9, 5.2, 4.5, and 5.8.

Sample ranges: 0.8, 1.2, 0.5, 0.3, 0.4, 0.9, 0.7, and 1.9.

Is this process in control?