At a major supermarket, checkout time is monitored to improve service quality. For six days, samples each with 20 observations have been obtained, and the following table summarizes the data. Determine if the checkout process is in control or not. You must show your analysis for the support of your decision.
Sample Mean Range
1 3.06 .42
2 3.15 .50
3 3.11 .41
4 3.13 .46
5 3.06 .46
6 3.09 .45