A production manager at a Contour Manufacturing plant has inspected the number o

Question

A production manager at a Contour Manufacturing plant has inspected the number of defective plastic molds in five random samples of 10 observations each. Following are the number of defective molds found in each sample:

Construct a 3-sigma control chart (z = 3) with this information. (If the lower control limit is negative, round the LCL to zero and all other answers to 2 decimal places, e.g. 15.25.)

Sample Number of
Defects Number of
Observations
in Sample 1 1 10 2 3 10 3 3 10 4 1 10 5 1 10 Total 9 50

Explanation / Answer

CL = Avg Fraction Defective = Total Number of Defects / Total Number of Observations = 9/50 = 0.18(avg p)

n = 9

STD of p = SQRT of [ p (1-p)/ n] = (.18)(.82)/9 = 0.13

UCL = Avg of p + 3 Std Error = Avg of p + 3 p =0.18 +3(.13) = 0.57

LCL = Avg of p - 3 Std Error = Avg of p - 3 p =0.18 - 3(.13) = - 0.21

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