A random sample of size n = 25 is taken from a population with mean μ = 20 and standard deviation σ = 10.

a. Construct the centerline and the upper and lower control limits for the chart.

b. Suppose six more samples of size 25 were drawn producing the following sample means: 18, 16, 19, 24, 28, and 30. Plot these values on the chart.

c. Are any points outside the control limits? Does it appear that the process is under control? Explain. L056