A health insurance company operates a 24/7 nurse advice line and is concerned about long call wait times. A time study team collected observations for the advice line?s answer time over a one-week period and the results are shown in the following table.

	Observation (seconds)
Day	1	2	3	4	5	6	7
1	46.5	37.2	31	26.4	24.6	22	21.2
2	8.4	12.1	18.7	18	15	13.7	12.5
3	9.5	8.3	10.6	8.5	7.2	8	7.5
4	8.2	22.6	25.2	30.5	20	22.8	21.5
5	25.6	24	19.3	19.3	17.8	18.2	17.8
6	9.7	12.5	9.3	12.8	14.8	12.5	9
7	19.5	11.5	7.3	20.2	16.8	14.1	8.2

a) Management is willing to use three-sigma limits. Use the given data, determine the control limits for an R -chart and an -chart.

b) Plot sample means and ranges on their respective control charts and interpret the results.

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