If the specification limits for the plastic pipes in Exercise 21.40 are LSL = 2.9 inches and USL = 3.1inches, determine the process capability index C_pk.

In exercise 21.40

Plastic pipe is used for plumbing in almost all new homes. If the pipes are too narrow or too wide, they will not connect properly with other parts of the plumbing system. A manufacturer of 3-inch diameter pipes uses statistical process control to maintain the quality of its products. The sampling plan is to draw samples of three 10-foot-long pipes every hour and measure the diameters. Twenty hours ago, the production process was shut down for repairs. The results of the first 20 samples taken since were recorded. Does it appear that the production process is under control?