A manufacturer of a particular grade of copper tubing collects data on the number of flaws occurring in 500 foot coils. Suppose they sample a total of 40 coils to initiate control charting. The average number of defects per coil is 2.5. The lower and upper control limits for the appropriate control chart for these data are
A) 0 and 7.24
B) 0 and 5.66
C) 2.24 and 7.24
D) 2.24 and 4.08
E) indeterminate

Question

Quizplus · Accepted Answer

The control chart for defects per unit is a c-chart. The upper control limit (UCL) is calculated as the average number of defects plus three times the square root of the average number of defects, and the lower control limit (LCL) is the average number of defects minus three times the square root of the average number of defects, but not less than zero. Here, UCL = 2.5 + 3√2.5 ≈ 7.24 and LCL = max(0, 2.5 - 3√2.5) = 0.

A Manufacturer of a Particular Grade of Copper Tubing Collects