Trinus Pipes and Tubes, a small company in Barrie, Ontario, produces plastic pipes certified to meet the Canadian Standards Association C448 specification for use in geothermal systems. Trinus provides 50-year warranties on its products against leakage, so the thickness of the pipe wall needs to be controlled carefully.

Suppose you work for a competing company and take four randomly selected samples of one-inch diameter pipes coming off the production line every hour for 10 hours. You measure the thickness of the pipe walls in thousandths of an inch and get the results in the data file ch24_MCSP_Pipe_Walls. Past records indicate that the thickness follows a Normal distribution.

Is the process in control? State your reasons clearly. Suppose the thickness of the pipe walls should be 0.100 plus/minus 0.005 inch. Are you meeting that requirement? State your assumptions clearly.