The factory described in problem 11-1 produces a second family of four parts in a manufacturing cell

Question:

The factory described in problem 11-1 produces a second family of four parts in a manufacturing cell that processes the parts in small batch quantities in sequence. Three parts are selected at random from each batch and measured for a critical characteristic. The sampling results for six production cycles are shown in the following table. It is known that the process variance is not the same for all products within the family.

a. Apply Equation 11-7 to these data to verify that the process variances cannot be assumed
to be the same for all product numbers.
Refer to attached Spreadsheet.
b. Construct a pair of stabilized control charts and determine the control status of this process.
c. The control charts are continued for an additional six cycles. The data are summarized in the table below. Has the control status for this process changed? Explain.