A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows from past experience that the process standard deviation is two ounces. Each day last week, he randomly selected four packages and weighed each. The data from that activity appear below. Weight Day Package 1 Package 2 Package 3 Package 4 Monday 23 22 23 24 Tuesday 23 21 19 21 Wednesday 20 19 20 21 Thursday 18 19 20 19 Friday 18 20 22 20

(a) Calculate all sample means and the mean of all sample means.

(b) Calculate upper and lower 2-sigma x-bar chart control limits that allow for natural variations.

(c) Based on the x-bar chart, is this process in control?