8.54 Production of ammeters is controlled for quality by periodically selecting an ammeter and obtaining four measurements on a test circuit designed to produce 15 amps. The data in table below were observed for 15 tested ammeters.

a Construct control limits for the mean by using the sample standard deviations.
b Do all observed sample means lie within the limits found in part (a)? If not, recalculate the control limits, omitting those samples that are “out of control.”
c Construct control limits for process variation and interpret the results.

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Reading Ammeter 1 2 3 4 12345 15.1 14.9 14.8 15.2 15.0 15.0 15.2 14.9 15.1 15.1 15.2 15.1 150 14.7 15.3 15.1 14.8 14.9 15.1 15.2 6 14.9 14.9 15.1 15.1 7 14.7 15.0 15.1 15.0 8 14.9 15.0 15.3 14.8 9 14.4 14.5 14.3 14.4 10 15.2 15.3 15.2 15.5 11 15.1 15.0 15.3 15.3 12 15.2 15.6 15.8 15.8 13 14.8 14.8 15.0 15.0 14 14.9 15.1 14.7 14.8 15 15.1 15.2 14.9 15.0