The manager of the Ace Motel wants to establish statistical control on the time it takes a maid to make up a room. The manager took random samples of 4 maids' performance every day for seven consecutive days. The results of the sample are as follow:

{Required:}
Construct the control charts and plot the samples. (Use the 3 -sigma control limit table.)

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Day 1 2 3 4 5 Sample Times (in minutes) 22, 16, 20, 28 20, 18, 22, 24 30, 20, 26, 22 24, 28, 30, 20 18, 28, 22, 28