1
Lesson 14 Statistical Process Control Solutions
Solved Problem #2: see textbook
Solved Problem #4: see textbook
Solved Problem #5: see textbook
Solved Problem #6: see textbook (manual problem)
#1:
Checkout time at a supermarket is monitored using a range and mean chart.
Six samples which contain
20 observations per sample have been collected and the sample means and sample ranges have been
computed as shown below.
Sample
Mean
Range
1
3.06
0.42
2
3.15
0.50
3
3.11
0.41
4
3.13
0.46
5
3.06
0.46
6
3.09
0.45
Perform the manual calculations necessary to answer the following questions.
a.
What is the sample size?
20
b.
Is the variability of the checkout time known or unknown?
Unknown
c.
Which chart is used to analyze the checkout time variability?
Range chart
d.
Which chart is used to analyze the checkout time?
Mean chart
e.
Should the range or mean chart be analyzed first?
Explain your answer.
Range chart should be analyzed before the mean chart because the variability of the process
must be in control before the mean chart can be analyzed.
Analyze the range chart by answering the following questions.
f.
What is the grand range?
.45
g.
Calculate the centerline, upper and lower control limits for the range chart?

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