Computer upgrades have a nominal time of 80 minutes. Samples of five observations each have been taken, and the results are as listed.
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Sample
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Observations
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1
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2
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3
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4
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5
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6
|
|
1
|
81
|
80.5
|
79.6
|
78.9
|
80.5
|
79.7
|
|
2
|
78.8
|
78.7
|
79.6
|
79.4
|
79.6
|
80.6
|
|
3
|
80
|
81
|
80.4
|
79.7
|
80.4
|
80.5
|
|
4
|
78.4
|
80.4
|
80.3
|
79.4
|
80.8
|
80
|
|
5
|
79.2
|
80.1
|
80.8
|
80.6
|
78.8
|
81.1
|
Question 1:
If we know the standard deviation of the process is σ = 2, z-score=3.
a. Using factors from the table above, determine upper and lower control limits for the mean chart, and decide if the process is in control.
b. Using factors from the table above, determine upper and lower control limits for the range chart, and decide if the process is in control.
Question 2:
If we don't know the standard deviation of the process.
a. Using factors from the table above, determine upper and lower control limits for the mean chart, and decide if the process is in control.
b. Using factors from the table above, determine upper and lower control limits for the range chart, and decide if the process is in control.
Question 3:
If we regard the operating time greater than 80 as a defective (i.e., > 80), calculate the three-sigma control limit of proportion (p) control chart, and decide if the process is in control.