Samples of n = 4 items are taken from a process at regular intervals. A normally distributed quality characteristic is measured and x and s values are calculated for each sample. After 50 subgroups have been analyzed, we have

(a) Compute the control limit for the x and s control charts
(b) Assume that all points on both charts plot within the control limits. What are the natural tolerance limits of the process?
(c) If the specification limits are 19 4.0, what are your conclusions regarding the ability of the process to produce items conforming to specifications?
(d) Assuming that if an item exceeds the upper specification limit it can be reworked, and if it is below the lower specification limit it must be scrapped, what percent scrap and rework is the process now producing?
(e) If the process were centered at µ = 19.0, what would be the effect on percent scrap and rework?

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Σ-= 1000; Σ S, = 72; m = 50 subgroups -1