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 8.70.
D) 2.24 and 4.08.
E) 0.80 and 8.70.

Question

Quizplus · Accepted Answer

The appropriate control chart for defect data (count data) is a c-chart, which is used for the number of defects per unit. The control limits for a c-chart are calculated using the formula: LCL = c - 3√c and UCL = c + 3√c, where c is the average number of defects per unit. Here, c = 2.5, so LCL = 2.5 - 3√2.5 ≈ -0.24 (but since the number of defects cannot be negative, we set LCL = 0), and UCL = 2.5 + 3√2.5 ≈ 7.24.

A Manufacturer of a Particular Grade of Copper Tubing Collects