Inter State Moving and Storage Company is setting up a control chart to monitor

Question

Inter State Moving and Storage Company is setting up a control chart to monitor the proportion of residential moves that result in written complaints due to late delivery, lost items, or damaged items. A sample of 55 moves is selected for each of the last 12 months. The number of written complaints in each sample is 9, 9, 4, 6, 1, 5, 11, 4, 8, 8, 8, and 15.

Insert the mean percent defective, UCL, and LCL. (Round your answers to 2 decimal places. Leave no cells blank - be certain to enter "0" wherever required.)

Inter State Moving and Storage Company is setting up a control chart to monitor the proportion of residential moves that result in written complaints due to late delivery, lost items, or damaged items. A sample of 55 moves is selected for each of the last 12 months. The number of written complaints in each sample is 9, 9, 4, 6, 1, 5, 11, 4, 8, 8, 8, and 15.

Explanation / Answer

Mean proportion defectives

P= Sum of defectives/ Sum of all samples = 88/660 =0.13 = center line of p chart

UCL = p+ 3 Sqrt(p(1-p)/n)
= 0.13+ 3Sqrt(0.13(1-0.13)/55
=0.26

LCL= p- 3 Sqrt(p(1-p)/n)
= 0.13 - 3Sqrt(0.13(1-0.13)/55
= - 0.006 ~ 0

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