4. Samples of size 5 are taken at regular intervals from a production process, and the values of the sample averages and sample standard deviations are calculated.

Suppose that the sum of the X and S values for the first 25 samples are given by

(a) Assuming control, determine the control limits for an X -control chart.

(b) Suppose that the measurable values of the items produced are supposed to be within the limits 14.3 ± .45. Assuming that the process remains in control with a mean and variance that is approximately equal to the estimates derived approximately what percentage of the items produced will fall within the specification limits?

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; = 357.2, 5; = 4.88