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home work problems
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Heizer/Render, Operations Management 7th Edition
Supplement 10 Internet Homework Problems
S10.31An assembly-line worker inserts Part A into Part B. A time study was conducted and produced the following results in seconds: 8.4, 8.6, 8.3, 8.5, 8.7, 8.5. What is the average cycle time?
S10.32 The cycle time for performing a certain task has been clocked at 10 minutes. The performance rating of the worker timed was estimated at 110%. Common practice in this department is to allow 5 minutes of personal time and 3 minutes of fatigue time per hour. In addition, there should be an extra allowance of 2 minutes per hour for inspection.
a)Find the normal time for the operation.
b)Compute the allowance factor and the standard time.
S10.33 The data in the following table represent time-study observations for an assembly process. On the basis of these observations, find the standard time for the process. Assume a 10% allowance factor.
Observations (minutes)
Performance
ElementRating (%)1234
5
11001.51.61.40.1*1.5
2902.32.52.12.22.4
31201.71.91.91.41.6
41003.53.63.63.63.2
*Disregardpossible error.
S10.34 An office worker has been clocked performing three work elements, with the results shown in the following table. The allowance for tasks such as this is 15%.
Observations (seconds)
Performance
Element123456Rating (%)
11311141651*15100
2 3*212573*2623110
3 3.0 3.3 3.1 2.9 3.4 2.8100
*Disregardpossible error.
a)Find the normal time.
b)Find the standard time.
S10.35 The data in the following table represent time-study observations for a metalworking process. On the basis of these observations, find the standard time for the process, assuming a 25% allowance factor.
Observations (minutes)
PerformanceElementRating (%)1234567
1901.801.701.661.911.851.771.60
21006.97.36.87.115.3*7.06.4
31153.09.0*9.5*3.82.93.13.2
49010.111.112.39.912.011.912.0
*Disregardemployee is smoking a cigarette (included in personal time).
S10.36 A time study has revealed an average observed time of 5 minutes, with a standard deviation of 1.25 minutes. These figures are based on a sample of 75 cycles. Is this sample large enough for an analyst to be 99.73% confident that the standard time is within 5% of the true value?
S10.37 The following data represent observations for a task in an assembly process. How many observations would be necessary for the observer to be 99% confident that the average task time is within 5% of the true value?
Observation (in minutes)
12345
1.51.61.41.51.5
(Hint: Compute the sample standard deviation as shown in Solved Problem S10.3.)
S10.38 Jell Lee Beans is famous for its boxed candies, which are sold primarily to businesses. About 30% of the candies are gift wrapped. One operator had the following observed times for gift wrapping in minutes: 2.2, 2.6, 2.3, 2.5, 2.4. What is the correct size if your accuracy is to be within 10% and your confidence level is 95.45%? If you desire an accuracy of 5% what would the sample size need to be?
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