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 1.5 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	24	22	22	20
Tuesday	20	20	18	22
Wednesday	21	19	17	19
Thursday	17	16	16	18
Friday	17	20	21	21

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

(b) Calculate upper and lower 3-sigma x-bar chart control limits that allow for natural variations.

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