Operations Management 12th. Edition by William J Stevenson | 9780078024108 | 0078024102

Operations Management

7 SOLVED PROBLEMS

193 SOLVED PROBLEMS

Question: C.5

A normal distribution has a mean of 20 and a standard deviation of 1.0. Find the probabilities: a. A value that is 22 or less. b. A value that is 22 or more. ...

Verified Answer:

First, determine the value of z for 22:

z=\...

Question: 17.p.3

A path in a network has three activities. Their standard deviations are 1.50, 0.80, and 1.30. Find the path standard deviation. ...

Verified Answer:

Standard deviations cannot be added, but variances...

Question: 7S.SP.2

A manager wants to determine an appropriate learning rate for a new type of work his firm will undertake. He has obtained completion times for the initial six repetitions of a job of this type. What learning rate is appropriate? ...

Verified Answer:

According to theory, the time per unit decreases a...

Question: 7.SP.2

A time study analyst wants to estimate the number of observations that will be needed to achieve a specified maximum error, with a confidence of 95.5 percent. A preliminary study yielded a mean of 5.2 minutes and a standard deviation of 1.1 minutes. Determine the total number of observations needed ...

Verified Answer:

a. A maximum error of ± 6 percent of the sample me...

Question: 7.SP.1

A time study analyst timed an assembly operation for 30 cycles, and then computed the average time per cycle, which was 18.75 minutes. The analyst assigned a performance rating of .96, and decided that an appropriate allowance was 15 percent. Assume the allowance factor is based on the workday. ...

Verified Answer:

OT = Average time = 18.75 minutes NT =  OT × Perfo...

Question: 4.SP.3

A hospital has three independent fire alarm systems, with reliabilities of .95, .97, and .99. In the event of a fire, what is the probability that a warning would be given? ...

Verified Answer:

A warning would not be given if all three alarms f...

Question: 4.SP.1

A product design engineer must decide if a redundant component is cost-justified in a certain system. The system in question has a critical component with a probability of .98 of operating. System failure would involve a cost of $20,000. For a cost of $100, a switch could be added that would ...

Verified Answer:

Because no probability is given for the switch, we...

Question: 6.4

Assign the six departments in Figure 6.12 to a 2 × 3 set of locations using the heuristic rule: Assign critical departments first, because they are the most important. ...

Verified Answer:

Critical pairs of departments are those with A or ...

Question: 10.4

An inspector counted the number of defective monthly billing statements of a telephone company in each of 20 samples. Using the following information, construct a control chart that will describe 99.74 percent of the chance variation in the process when the process is in control. Each sample ...

Verified Answer:

To find z, divide .9974 by 2 to obtain .4987, and ...

Question: 7S.P.1

An assembly operation has a 90 percent learning curve. The line has just begun work on a new item; the initial unit required 28 hours. Estimate the time that will be needed to complete: a. The first five units. b. Units 20 through 25. ...

Verified Answer:

Use the total time factor in the 90 percent column...

Question: 17.7

Using the following information, develop the optimal time–cost solution. Project costs are $1,000 per day. ...

Verified Answer:

a. Determine which activities are on the critical ...

Question: 7S.4

Use learning curve theory to predict the number of repetitions (units) that will be needed for a trainee to achieve a unit time of 6 minutes if the trainee took 10 minutes to do the first unit and a learning curve of 90 percent is operative. a. Use the learning table. b. Use the log formula. ...

Verified Answer:

a. The table approach can be used for the learning...

Question: 7.P.2

A time study analyst wants to estimate the number of observations that will be needed to achieve a specified maximum error, with a confidence of 95.5 percent. A preliminary study yielded a mean of 5.2 minutes and a standard deviation of 1.1 minutes. Determine the total number of observations needed ...

Verified Answer:

a. A maximum error of ± 6 percent of the sample me...

Question: 7S.3

The manager in Example 7S–2 believes that some unusual problems were encountered in producing the first jet and would like to revise that estimate based on a completion time of 276 days for the third jet. ...

Verified Answer:

The unit value for n = 3 and an 80 percent curve i...

Question: 17.5

The network diagram for a project is shown in the accompanying figure, with three time estimates for each activity. Activity times are in weeks. Do the following: a. Compute the expected time for each activity and the expected duration for each path. b. Identify the critical path. c. Compute the ...

Verified Answer:

a. b. The path that has the longest expected durat...

Question: 7S.2

Production Airplanes is negotiating a contract for the production of 20 small jet aircraft. The initial jet required the equivalent of 400 days of direct labor. The learning percentage is 80 percent. Estimate the expected number of days of direct labor for a. The 20th jet. b. All 20 jets. c. The ...

Verified Answer:

Using Table 7S.1 with n = 20 and an 80 percent lea...

Question: 17.4

Compute slack times for the preceding example. ...

Verified Answer:

Either the starting times or the finishing times c...