Chapter 13.6, Problem 13.51ACI

Leaky process pumps. Quality (February 2008) presented a problem that actually occurred at a company that produces process pumps for a variety of industries. The company recently introduced a new pump model and immediately began receiving customer complaints about “leaky pumps.” There were no complaints about the old pump model. For each of the first 13 weeks of production of the new pump, quality-control inspectors tested 500 randomly selected pumps for leaks. The results of the leak tests are summarized by week in the accompanying table. Construct an appropriate control chart for the data. What does the chart indicate about the stability of the process?

	Week	Number Tested	Number with Leaks
	1	500	36
	2	500	28
	3	500	24
	4	500	26
	5	500	20
	6	500	56
	7	500	26
	8	500	28
	9	500	31
	10	500	26
	11	500	34
	12	500	26
	13	500	32