Random samples of size n=25 are taken from a normally distributed population with mean =20 and

Random samples of size n=25 are taken from a normally distributed population with mean µ =20 and standard deviation σ =10.

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

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

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