8.66 An aircraft subassembly paint shop has the task of painting a variety of reworked aircraft parts.

Some parts are large and require hours to paint, whereas some are small and can be painted in a few minutes. Rather than looking at paint defects per part as a quality-improvement tool, it was decided to group parts together and look at paint defects over a period of hours worked. Data in this form are given in table below for a sequence of 20 samples. Construct an appropriate control chart for these data. Does it look as if the painting process is in control?

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Sample Defects Hours Sample Defects Hours 1234567 4 51.5 11 1 38.8 1 51.5 12 0 47.1 13 0 47.1 14 2 53.1 15 3020 57.8 39.1 49.1 41.6 3 40.4 16 1 51.5 0 57.7 17 1 42.1 8 0 51.5 18 2 54.3 9 0 34.8 19 1 36.6 10 1 51.5 20 0 36.6