Shewhart chart of continuous data. A critical contaminant is regularly monitored on a run chart during continuous production of a chemical. Samples are selected three times (at somewhat regular intervals) during each eight-hour shift. The process engineer wanted to plan a study to evaluate some modifications to the process. She obtained the following data during the last week:

(a) Develop a Shewhart chart for these data. How should the data be subgrouped?

(b) Was the process stable during this week?

(c) Plan an experiment to study a modification to one of the raw materials used in this process.

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Concentration of contaminant (ppm) A shift B shift C shift Monday 18 17 18 17 20 18 17 18 16 Tuesday 19 16 18 19 17 19 18 16 19 Wednesday 17 16 20 17 18 19 17 19 18 Thursday 17 21 21 18 22 20 16. 22 21 Friday 24 21 22 22 21 22 23 22 22 Saturday 20 20 23 21 22 22 23 22 22 Sunday 21 21 22 20 21 22 22 21 20