Class 13 problems for class Solutions.docx

# Class 13 problems for class Solutions.docx - 1 1[Chapter 10...

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1 1. [Chapter 10, problem 6]: Using four samples of 200 credit card statements each, an auditor found the following number of erroneous statements in each sample. Sample number 1 2 3 4 # of errors 4 2 5 9 a. Determine the proportion of defectives in each sample. b. If the true proportion of defectives for this process is unknown, what is your best estimate of it? c. What is your estimate of the mean and standard deviation of the sampling distribution of the sample proportion of defectives for samples of 200? d. What control limits would give an alpha risk of 0.03 for this process? e. What alpha risk would control limits of 0.047 and 0.003 provide? f. Using the control limits of 0.047 and 0.003, is the process in control? g. Suppose the long term proportion of defectives of the process is known to be 2%. What are the values of the mean and standard deviation of the sampling distribution? h. Construct a control chart for the process, assuming a proportion of defectives of 2% and two sigma control limits. Is this process in control? Solution n = 200 a. Sample 1 Sample 2 Sample 3 Sample 4 4 = .020 2 = .010 5 = .025 9 = .045 200 200 200 200 b. (0.02 + 0.01 + 0.025 + 0.045) / 4 = 0.025 c. mean = .025

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2 011 . 200 ) 975 (. 025 . ) 1 ( . dev Std. n p p d. α = 0.03 confidence = .97 (two-sided) z = 2.17 .025 ± 2.17(0.011) = .025 ± .024 = .001 to .049.
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• Fall '11
• Management, Control Chart, UCL, LCL

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