A paper mill uses a control chart to monitor the imperfection nin finished rolls of paper. Production output is inspected for 20 days, and the resulting data are shown in Table 7E.13. Use these data to set up a control chart for nonconformities per roll of paper. Does the process appear to be in statistical control? What center line and control limits would you recommend for controlling current production?

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TABLE 7E.13 Data on Imperfections in Rolls of Paper Total Total Number Number of Number Number of of Rells Imper- of RellsImper- Day Produced fections Day Produced fections 1 18 18 3 24 4 22 5 22 6 22 7 20 8 20 9 20 0 20 12 14 20 I8 15 12 18 18 18 14 20 15 20 16 20 17 24 18 24 19 22 18 12 13 2 10 15 12 10 16 18 20 17