Refer to the freezer problem 17.51 with μ = 23 and σ = 2. Temperature measurements are recorded four times a day (at midnight, 0600, 1200, and 1800). Twenty samples of four - observations are shown below.
(a) Construct upper and lower control limits for the x chart, using the given process parameters.
(b) Plot the data on the control chart.
(c) Is this process in control? Explain your reasoning.