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Practical Management Science

Wayne L. Winston, S. Christian Albright

Chapter 5

Network Models - all with Video Answers

Educators


Chapter Questions

03:55

Problem 1

In the original Grand Prix example, the total capacity of the three plants is 1550 , well above the total customer demand. Would it help to have 100 more units of capacity at plant 1 ? What is the most Grand Prix would be willing to pay for this extra capacity? Answer the same questions for plant 2 and for plant 3 . Explain why extra capacity can be valuable even though the company already has more total capacity than it requires.

Hongchang Guo
Hongchang Guo
Numerade Educator
01:30

Problem 2

The optimal solution to the original Grand Prix problem indicates that with a unit shipping cost of $$\$ 132$$, the route from plant 3 to region 2 is evidently too expensive-no autos are shipped along this route. Use SolverTable to see how much this unit shipping cost would have to be reduced before some autos would be shipped along this route.

Carson Merrill
Carson Merrill
Numerade Educator
15:48

Problem 3

Suppose in the original Grand Prix example that the routes from plant 2 to region 1 and from plant 3 to region 3 are not allowed. (Perhaps there are no railroad lines for these routes.) How would you modify the original model (Figure 5.2) to rule out these routes? How would you modify the alternative model (Figure 5.7) to do so? Discuss the pros and cons of these two approaches.

Carlos Pinilla
Carlos Pinilla
Numerade Educator
03:05

Problem 4

In the Grand Prix example with varying tax rates, the optimal solution more than satisfies customer demands. Modify the model so that regions have not only lower limits on the amounts they require, but upper limits on the amounts they can sell. Assume these upper limits are 50 autos above the required lower limits. For example, the lower and upper limits for region 1 are 450 and 500 . Modify the model and find the optimal solution. How does it differ from the solution without upper limits?

Lucas Finney
Lucas Finney
Numerade Educator
04:03

Problem 5

In the Grand Prix example with varying tax rates, the optimal solution uses all available plant capacity and more than satisfies customer demands. Will this always be the case? Experiment with the unit selling prices and/or tax rates to see whether the company ever uses less than its total capacity.

Md.Daniyal Arshad
Md.Daniyal Arshad
Numerade Educator

Problem 6

Here is a problem to challenge your intuition. In the original Grand Prix example, reduce the capacity of plant 2 to 300 . Then the total capacity is equal to the total demand. Reoptimize the model. You should find that the optimal solution uses all capacity and exactly meets all demands with a total cost of $$\$ 176,050$$. Now increase the capacity of plant 1 and the demand at region 2 by 1 automobile each, and optimize again.
What happens to the optimal total cost? How can you explain this "more for less" paradox?

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01:03

Problem 7

Continuing the previous problem (with capacity 300 at plant 2), suppose we want to see how much extra capacity and extra demand we can add to plant 1 and region 2 (the same amount to each) before the total shipping cost stops decreasing and starts increasing. Use SolverTable appropriately to find out. (You will probably need to use some trial and error on the range of input values.) Can you explain intuitively what
causes the total cost to stop decreasing and start increasing?

Carson Merrill
Carson Merrill
Numerade Educator
06:13

Problem 8

Modify the original Grand Prix example as follows. Increase the demands at the regions by 200 each, so that total demand is well above total plant capacity. However, now interpret these "demands" as "maximum sales," the most each region can accommodate, and change the "demand" constraints to become "s" constraints, not " $\geq$ " constraints. How does the optimal solution change? Does it make realistic sense? If not, how might you change the model to obtain a realistic solution?

Jessica Wellington
Jessica Wellington
University of Missouri - Columbia
01:31

Problem 9

Modify the original Grand Prix example as follows. Increase the demands at the regions by 200 each, so that total demand is well above total plant capacity. This means that some demands cannot be supplied. Suppose there is a unit "penalty" cost at each region for not supplying an automobile. Let these unit penalty costs be $$\$ 600, \$ 750, \$ 625$$, and $$\$ 550$$ for the four regions. Develop a model to minimize the sum of shipping costs and penalty costs for unsatisfied demands.

Colin O'Haire
Colin O'Haire
Numerade Educator
00:21

Problem 10

Modify the machine-to-job assignment model under the assumption that only three of the four jobs must be completed. In other words, one of the four jobs does not have to be assigned to any machine. What is the new optimal solution?

Clarissa Noh
Clarissa Noh
Numerade Educator

Problem 11

One possible solution method for the machine-to-job assignment problem is the following heuristic procedure. Assign the machine to job 1 that completes job 1 quickest. Then assign the machine to job 2 that, among all machines that still have some capacity, completes job 2 quickest. Keep going until a machine has been assigned to all jobs. Does this heuristic procedure yield the optimal solution for this problem? If it does, see whether you can change the job times so that the heuristic does not yield the optimal solution.

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01:24

Problem 12

In the machine-to-job assignment problem, the current capacities of the machines are $1,2,1,2$, and 1 . If you could increase one of these capacities by 1 , which would you increase? Why?

Shahab Ullah
Shahab Ullah
Numerade Educator
07:56

Problem 13

Modify the bus route assignment model, assuming that company 1 decides to place bids on routes 7 and 8 (in addition to its current bids on other routes). The bids on these two routes are $$\$ 5200$$ and $$\$ 3300$$. Does the optimal solution change?

MM
Matthys Marthinus
Numerade Educator

Problem 14

We modeled the bus route assignment problem with the alternative form of the transportation model (as in Figure 5.7). Model it instead with the "standard" form (as in Figure 5.2). Discuss the pros and cons of these two approaches for this particular example.

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Problem 15

In the optimal solution to the machine-to-job assignment problem, jobs 1 and 2 are both assigned to machine 4. Suppose we impose the restriction that jobs 1 and 2 must be assigned to different machines. Change the model to accommodate this restriction and find the new optimal solution.

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Problem 16

In the optimal solution to the machine-to-job assignment problem, jobs 3 and 4 are assigned to different machines. Suppose we impose the restriction that these jobs must be assigned to the same machine. Change the model to accommodate this restriction and find the new optimal solution.

James Kiss
James Kiss
Numerade Educator

Problem 17

In the optimal solution to the bus route assignment problem, company 2 is assigned to bus routes 6 and 7 . Suppose these two routes are far enough apart that it is infeasible for one company to service both of them. Change the model to accommodate this restriction and find the new optimal solution.

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Problem 18

When we (the authors) originally developed the bus route assignment model, we included an arc capacity constraint: Flow $\leq 1$. After giving this further thought, we deleted this constraint as being redundant. Why could we do this? Specifically, why can't one or more of the flows found by Solver be greater than 1? (Hint: Think in terms of flows out of and into the nodes in the network diagram.)

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08:13

Problem 19

In the original RedBrand problem, suppose the plants cannot ship to each other and the customers cannot ship to each other. Modify the model appropriately and reoptimize. How much does the total cost increase because of these disallowed routes?

Jacquelyn Trost
Jacquelyn Trost
Numerade Educator

Problem 20

Modify the original RedBrand problem so that all flows must be from plants to warehouses and
from warehouses to customers. Disallow all other arcs. How much does this restriction cost
RedBrand, relative to the original optimal shipping cost?

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02:47

Problem 21

In the original RedBrand problem, the costs for shipping from plants or warehouses to customer 2 were purposely made high so that it would be optimal to ship to customer 1 and then let customer 1 ship to customer 2. Use SolverTable appropriately to do the following. Decrease the unit shipping costs from plants and warehouses to customer 1 , all by the same amount, until it is no longer optimal for customer 1 to ship to customer 2. Describe what happens to the optimal shipping plan at this point.

Victoria Dollar
Victoria Dollar
Numerade Educator
01:11

Problem 22

In the original RedBrand problem, we assume a constant arc capacity, the same for all allowable arcs. Modify the model so that each are has its own arc capacity. You can make up the required arc capacities.

Ashley High
Ashley High
Numerade Educator
01:54

Problem 23

Continuing the previous problem, make the problem even more general by allowing upper bounds (arc capacities) and lower bounds for the flows on the allowable arcs. Some of the upper bounds can be very large numbers, effectively indicating that there is no arc capacity for these arcs, and the lower bounds can be 0 or positive. If they are positive, then they indicate that some positive flow must occur on these arcs. Modify the model appropriately to handle these upper and lower bounds. You can make up the required bounds.

R M
R M
Numerade Educator
04:44

Problem 24

Expand the RedBrand two-product spreadsheet model so that there are now three products competing for the arc capacity. You can make up the required input data.

Natalie Britton
Natalie Britton
Numerade Educator

Problem 25

In the RedBrand two-product problem, we assumed that the unit shipping costs are the same for both products. Modify the spreadsheet model so that each product has its own unit shipping costs. You can assume that the original unit shipping costs apply to product 1 , and you can make up new unit shipping costs for product 2 .
Skill-Extending Problems

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Problem 26

How difficult is it to expand the original RedBrand model? Answer this by adding a new plant, two new
warehouses, and three new customers, and modify the spreadsheet model appropriately. You can make up the required input data.

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06:30

Problem 27

In the RedBrand problem with shrinkage, change the assumptions. Now instead of assuming that there is some shrinkage at the warehouses, assume that there is shrinkage in delivery along each route. Specifically, assume that a certain percentage of the units sent along each arc perish in transit-from faulty refrigeration, say-and this percentage can differ from one arc to another. Modify the model appropriately to take this type of behavior into account. You can make up the shrinkage factors, and you can assume that arc capacities apply to the amounts originally shipped, not to the amounts after shrinkage. (Make sure your input data permit a feasible solution. After all, if there is too much shrinkage, it will be impossible to meet demands with available plant capacity. Increase the plant capacities if necessary.)

Raymond Matshanda
Raymond Matshanda
Numerade Educator
02:38

Problem 28

Consider a modification of the original RedBrand problem where there are $N$ plants, $M$ warehouses, and $L$ customers. Assume that the only allowable ares are from plants to warehouses and from warehouses to customers. If all such arcs are allowable-all plants can ship to all warehouses and all warehouses can ship to all customers - how many changing cells are in the spreadsheet model? Keeping in mind that Excel's Solver can handle at most 200 changing cells, give some combinations of $N, M$, and $L$ that will just barely stay within Solver's limit.

Nick Johnson
Nick Johnson
Numerade Educator

Problem 29

Continuing the previous problem, develop a sample model with your own choices of $N, M$, and $L$ that barely stay within Solver's limit. You can make up any input data. The important point here is the layout and formulas of the spreadsheet model.

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Problem 30

In Maude's shortest path problem, suppose all arcs in the current network from higher-numbered nodes to lower-numbered nodes, such as from node 6 to node 5 , are disallowed. Modify the spreadsheet model and find the shortest path from node 1 to node 10 . Is it the same as before? Should you have known the answer to this question before making any changes to the original model? Explain.

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Problem 31

In Maude's shortest path problem, suppose all arcs in the network are "double-arrowed," that is, Maude can travel along each arc (with the same distance) in either direction. Modify the spreadsheet model appropriately. Is her optimal solution still the same?

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Problem 32

Continuing the previous problem, suppose again that all ares go in both directions, but suppose Maude's objective is to find the shortest path from node 1 to node 7 (not node 10). Modify the spreadsheet model appropriately and solve.

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01:57

Problem 33

How difficult is it to add nodes and arcs to an existing shortest path model? Answer by adding a new node, node 11, to Maude's network. Assume that node 11 is at the top of the network, geographically, with double-arrowed arcs joining it to nodes 2,5 , and 7 with distances 45,22 , and 10. Assume that Maude's
objective is still to get from node 1 to node 10 . Does the new optimal solution go through node 11 ?

WZ
Wen Zheng
Numerade Educator
02:48

Problem 34

In the VanBuren machine replacement problem, we assumed that the maintenance cost and salvage values are linear functions of age. Suppose instead that the maintenance cost increases by $50 \%$ each quarter and that the salvage value decreases by $10 \%$ each quarter. Rework the model with these assumptions. What is the optimal replacement schedule?

Kaylee Mcclellan
Kaylee Mcclellan
Numerade Educator
01:20

Problem 35

In the VanBuren machine replacement problem, the company's current policy is to keep a machine at least 4 quarters but no more than 12 quarters. Suppose this policy is instead to keep a machine at least 5 quarters but no more than 10 quarters. Modify the spreadsheet model appropriately. Is the new optimal solution the same as before?

Nick Johnson
Nick Johnson
Numerade Educator
01:20

Problem 36

In the VanBuren machine replacement problem, the company's current policy is to keep a machine at least 4 quarters but no more than 12 quarters.
Suppose instead that the company imposes no upper limit on how long it will keep a machine; its only policy requirement is that a machine must be kept at least 4 quarters. Modify the spreadsheet model appropriately. Is the new optimal solution the same as before?

Nick Johnson
Nick Johnson
Numerade Educator
04:14

Problem 37

In the VanBuren machine replacement problem, suppose the company starts with a machine that is eight quarters old at the beginning of the first quarter. Modify the model appropriately, keeping in mind that this initial machine must be sold no more than four quarters from now.

Vikash Ranjan
Vikash Ranjan
Numerade Educator
01:11

Problem 38

We illustrated how a machine replacement problem can be modeled as a shortest path problem. This is probably not the approach most people would think of when they first see a machine replacement problem. In fact, most people would probably never think in terms of a network. How would you model the problem? Does your approach result in an LP model?

Hunza Gilgit
Hunza Gilgit
Numerade Educator
06:11

Problem 39

In the crew-scheduling problem, suppose (as in the sensitivity analysis we discussed) that the first Chicago flight, $\mathrm{C}$, is delayed by 2 hours - that is, its departure and arrival times move up to 8 A.M. and 12 P.M., respectively. How does the model need to be modified? What is the new optimal solution? Is it the same as the solution indicated by SolverTable in Figure 5.35 ? If not, why not?

Carson Merrill
Carson Merrill
Numerade Educator

Problem 40

The required downtime in the crew-scheduling problem is currently assumed to be 1 hour. Suppose we instead require it to be 2 hours. How does the model need to be modified? What is the new optimal solution?

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01:26

Problem 41

In the crew-scheduling problem, suppose that two extra flights are added to the current list. The first leaves Chicago at 11 A.M. and arrives in New York at 2 P.M. The second leaves New York at 6 P.M. and arrives in Chicago at 8 P.M. (Remember that all quoted times are EST.) Modify the model to incorporate these two new flights. What is the new optimal solution?

A M
A M
Numerade Educator
03:01

Problem 42

In the flight-scheduling model, use SolverTable to examine the effect of decreasing all net revenues by the same percentage, assuming that the company owns 6 planes. Let this percentage vary from $0 \%$ to $50 \%$ in increments of $10 \%$. Discuss the changes that occur in the optimal solution.

Carson Merrill
Carson Merrill
Numerade Educator
02:32

Problem 43

In the flight-scheduling model, use SolverTable to examine the effect of increasing both the fixed cost per plane and the overnight cost by the same percentage, assuming that the company owns 8 planes. Let this percentage vary from $0 \%$ to $50 \%$ in increments of $10 \%$. Discuss the changes that occur in the optimal solution.
Skill-Extending Problems

AG
Ankit Gupta
Numerade Educator
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Problem 44

One rather unrealistic assumption in the flightscheduling model is that a given plane can fly two consecutive flights with no downtime. For example, it could fly flight 5903 that gets into Washington, D.C. at time 14 and then fly flight 7555 that leaves Washington, D.C. at time 14. Modify the model so that there must be at least 1 hour of downtime between consecutive flights.

Gregory Devenport
Gregory Devenport
Numerade Educator
01:26

Problem 45

In the crew-scheduling model, there are exactly as many flights departing from Chicago as departing from New York. Suppose more flights are departing from one city than from the other. How would you model this? Illustrate by assuming that there is an extra flight from Chicago that leaves at 11 A.M. and arrives at New York at 2 P.M. (Remember that all quoted times are EST.)

A M
A M
Numerade Educator
01:27

Problem 46

The 7th National Bank has two check-processing sites. Site 1 can process 10,000 checks per day, and site 2 can process 6000 checks per day. The bank processes three types of checks: vendor, salary, and personal. The processing cost per check depends on the site, as listed in the file P05_46.xIsx. Each day, 5000 checks of each type must be processed. Determine how to minimize the daily cost of processing checks.

Heather Zimmers
Heather Zimmers
Numerade Educator
03:35

Problem 47

The government is auctioning off oil leases at two sites: 1 and 2. At each site, 100,000 acres of land are to be auctioned. Cliff Ewing, Blake Barnes, and Alexis Pickens are bidding for the oil. Government rules state
that no bidder can receive more than $40 \%$ of the land being auctioned. Cliff has bid $$\$ 1000$$ per acre for site 1 land and $$\$ 2000$$ per acre for site 2 land. Blake has bid $$\$ 900$$ per acre for site 1 land and $$\$ 2200$$ per acre for site 2 land. Alexis has bid $$\$ 1100$$ per acre for site 1 land and $$\$ 1900$$ per acre for site 2 land.
a. Determine how to maximize the government's revenue with a transportation model.
b. Use SolverTable to see how changes in the government's rule on $40 \%$ of all land being auctioned affect the optimal revenue. Why can the optimal revenue not decrease if this percentage required increases? Why can the optimal revenue not increase if this percentage required decreases?

Niamat Khuda
Niamat Khuda
Numerade Educator
10:45

Problem 48

The Amorco Oil Company controls two oil fields. Field 1 can produce up to 40 million barrels of oil per day, and field 2 can produce up to 50 million barrels of oil per day. At field 1 , it costs $$\$ 37.50$$ to extract and refine a barrel of oil; at field 2 the cost is $$\$ 41.20$$. Amorco sells oil to two countries: United Kingdom and Japan. The shipping costs per barrel are shown in the file P05_48.xlsx. Each day, the United Kingdom is willing to buy up to 40 million barrels at $$\$ 65.80$$ per barrel, and Japan is willing to buy up to 30 million barrels at $$\$ 68.40$$ per barrel. Determine how to maximize Amorco's profit.

Jacquelyn Trost
Jacquelyn Trost
Numerade Educator
05:35

Problem 49

Touche Young has three auditors. Each can work up to 160 hours during the next month, during which time three projects must be completed. Project 1 takes 130 hours, project 2 takes 140 hours, and project 3 takes 160 hours. The amount per hour that can be billed for assigning each auditor to each project is given in the file $\mathrm{P} 05 \_49 . x \mathrm{x} x$. Determine how to maximize total billings during the next month.

Foster Wisusik
Foster Wisusik
Numerade Educator
00:21

Problem 50

Five employees are available to perform four jobs. The time it takes each person to perform each job is given in the file P05_50.xIsx. Determine the assignment of employees to jobs that minimizes the total time required to perform the four jobs. (A dash indicates that a person cannot do that particular job.)

Clarissa Noh
Clarissa Noh
Numerade Educator
04:58

Problem 51

Based on Machol (1970). Doc Councilman is putting together a relay team for the 400 -meter relay. Each swimmer must swim 100 meters of breaststroke, backstroke, butterfly, or freestyle, and each swimmer can swim only one race. Doc believes that each swimmer will attain the times given in the file P05_51.xlsx. To minimize the team's time for the race, which swimmers should swim which strokes?

Bryan Meares
Bryan Meares
Numerade Educator
02:44

Problem 52

A company is taking bids on four construction jobs. Three contractors have placed bids on the jobs. Their bids (in thousands of dollars) are given in the file P05_52.xlsx. (A dash indicates that the contractor did not bid on the given job.) Contractor 1 can do only one job, but contractors 2 and 3 can each do up to two jobs. Determine the minimum cost assignment of contractors to jobs.

Sheryl Ezze
Sheryl Ezze
Numerade Educator
03:31

Problem 53

Widgetco manufactures widgets at two factories, one in Memphis and one in Denver. The Memphis factory can produce up to 150 widgets per day, and the Denver factory can produce up to 200 widgets per day. Widgets are shipped by air to customers in Los Angeles and Boston. The customers in each city require 130 widgets per day. Because of the deregulation of airfares, Widgetco believes that it might be cheaper to first fly some widgets to New York or Chicago and then fly them to their final destinations. The costs of flying a widget are shown in the file P05 53.xlsx.
a. Determine how to minimize the total cost of shipping the required widgets to the customers.
b. Suppose the capacities of both factories are reduced in increments of 10 widgets per day. Use SolverTable to see how much the common reduction can be before the total cost increases; before there is no feasible solution.

Breanna Ollech
Breanna Ollech
Numerade Educator
02:00

Problem 54

General Ford produces cars in Los Angeles and Detroit and has a warehouse in Atlanta. The company supplies cars to customers in Houston and Tampa. The costs of shipping a car between various points are listed in the file P05 54.xIsx, where a dash means that a shipment is not allowed. Los Angeles can produce up to 1100 cars, and Detroit can produce up to 2900 cars. Houston must receive 2400 cars, and Tampa must receive 1500 cars.
a. Determine how to minimize the cost of meeting demands in Houston and Tampa.
b. Modify the answer to part a if shipments between Los Angeles and Detroit are not allowed.
c. Modify the answer to part a if shipments between Houston and Tampa are allowed at a cost of $\$ 5 \mathrm{per}$ car.

Jennifer Stoner
Jennifer Stoner
Numerade Educator
09:16

Problem 55

Sunco Oil produces oil at two wells. Well 1 can produce up to 150,000 barrels per day, and well 2 can produce up to 200,000 barrels per day. It is possible to ship oil directly from the wells to Sunco's customers in Los Angeles and New York. Alternatively, Sunco could transport oil to the ports of Mobile and Galveston and then ship it by tanker to New York or Los Angeles. Los Angeles requires 160,000 barrels per day, and New York requires 140,000 barrels per day. The costs of shipping 1000 barrels between various locations are shown in the file P05_55.xlsx, where a dash indicates shipments that are not allowed. Determine how to minimize the transport costs in meeting the oil demands of Los Angeles and New York.

Alvar Garcia-Fernandez
Alvar Garcia-Fernandez
Numerade Educator
03:08

Problem 56

Nash Auto has two plants, two warehouses, and three customers. The plants are in Detroit and Atlanta, the warehouses are in Denver and New York, and the customers are in Los Angeles, Chicago, and Philadelphia. Cars are produced at plants, then shipped to warehouses, and finally shipped to customers. Detroit can produce 150 cars per week, and Atlanta can produce 100 cars per week. Los Angeles requires 80 cars per week, Chicago requires 70 , and Philadelphia requires 60. It costs $$\$ 10,000$$ to produce a car at each plant. The costs of shipping a car between various cities are listed in the file P05_56.xlsx. Assume that during a week, at most 50 cars can be shipped from a warehouse to any particular city. Determine how to meet Nash's weekly demands at minimum cost.

Victoria Dollar
Victoria Dollar
Numerade Educator
03:08

Problem 57

Fordco produces cars in Detroit and Dallas. The Detroit plant can produce up to 6500 cars, and the Dallas plant can produce up to 6000 cars. Producing a car costs $$\$ 2000$$ in Detroit and $$\$ 1800$$ in Dallas. Cars must be shipped to three cities. City 1 must receive 5000 cars, city 2 must receive 4000 cars, and city 3 must receive 3000 cars. The costs of shipping a car from each plant to each city are given in the file P05_57.xlsx. At most 2700 cars can be sent from a given plant to a given city. Determine how to minimize the cost of meeting all demands.

Victoria Dollar
Victoria Dollar
Numerade Educator
01:15

Problem 58

Each year, Data Corporal produces up to 400 computers in Boston and up to 300 computers in Raleigh. Los Angeles customers must receive 400 computers, and 300 computers must be supplied to Austin customers. Producing a computer costs $$\$ 350$$ in Boston and $$\$ 400$$ in Raleigh. Computers are transported by plane and can be sent through Chicago. The costs of sending a computer between pairs of cities are shown in the file P05 58.xlsx.
a. Determine how to minimize the total (production plus distribution) cost of meeting Data Corporal's annual demand.
b. How would you modify the model in part a if at most 200 units could be shipped through Chicago?

Carson Merrill
Carson Merrill
Numerade Educator
00:47

Problem 59

Suppose it costs $$\$ 10,000$$ to purchase a new car. The annual operating cost and resale value of a used car are shown in the file P05 59.xlsx. Assume that you presently have a new car. Determine a replacement policy that minimizes your net costs of owning and operating a car for the next six years.

Sneha Ravi
Sneha Ravi
Numerade Educator
03:08

Problem 60

It costs $$\$ 200$$ to buy a lawn mower from a lawn supply store. Assume that I can keep a lawn mower for at most 5 years and that the estimated maintenance cost each year of operation is as follows: year 1, $$\$ 50$$; year $$2, \$ 80$$; year $$3, \$ 140$$; year $$4, \$ 160$$; year $$5, \$ 180$$. I have just purchased a new lawn mower. Assuming that a lawn mower has no salvage value, determine the strategy that minimizes the total cost of purchasing and operating a lawn mower for the next 10 years.

Erica Bischoff
Erica Bischoff
Numerade Educator
00:56

Problem 61

At the beginning of year 1 , a new machine must be purchased. The cost of maintaining a machine, depending on its age, is given in the file $\mathrm{P} 05$ 61.xlsx. The cost of purchasing a machine at the beginning of each year is given in this same file. There is no tradein value when a machine is replaced. The goal is to minimize the total (purchase plus maintenance) cost of having a machine for 5 years. Determine the years in which a new machine should be purchased.

Lauren Shelton
Lauren Shelton
Numerade Educator

Problem 62

The town of Busville has three school districts. The numbers of black students and white students in each district are shown in the file P05_62.xlsx. The Supreme Court requires the schools in Busville to be racially balanced. Thus, each school must have exactly 300 students, and each school must have the same number of black students. The distances between districts are also shown in the file P05_62.xlsx. Determine how to minimize the total distance that students must be bussed while still satisfying the Supreme Court's requirements. Assume that a student who remains in his or her own district does not need to be bussed.

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02:58

Problem 63

Delko is considering hiring people for four types of jobs. The company would like to hire the number of people listed in the file P05_63.xIsx for each type of job. Delko can hire four types of people. Each type is qualified to perform two types of jobs, as shown in this same file. A total of 20 type 1,30 type 2, 40 type 3 , and 20 type 4 people have applied for jobs. Determine how Delko can maximize the number of employees assigned to suitable jobs, assuming that each person can be assigned to at most one job. (Hint: Set this up as a transportation model where the "supplies" are the applicants.)

Carson Merrill
Carson Merrill
Numerade Educator
01:25

Problem 64

A truck must travel from New York to Los Angeles. As shown in Figure 5.46, several routes are available. The number associated with each arc is the number of gallons of fuel required by the truck to traverse the arc. Determine the route from New York to Los Angeles that uses the minimum amount of gas.

Anna Jones
Anna Jones
Numerade Educator
03:55

Problem 65

We are trying to help the MCSCC (Monroe County School Corporation) determine the appropriate high school district for each housing development in Bloomington. For each development, we are given the number of students, the mean family income, the percentage of minorities, and the distance to each high school (South and North). These data are listed in the file P05_65,xlsx. In assigning the students, MCSCC wants to minimize total distance traveled subject to the following constraints:
- Each school must have at least 1500 students.
- The mean family income must be at least $$\$ 85,000$$ for students of each school.
- Each school must have at least $10 \%$ minorities.
Determine an optimal assignment of students to schools. Then provide a one-paragraph summary of how the optimal solution changes as the required minority percentage varies from $5 \%$ to $11 \%$.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:26

Problem 66

A school system has 16 bus drivers that must cover 12 bus routes. Each driver can cover at most one route. The driver's bids for the various routes are listed in the file P05_66.xlsx. Each bid indicates the amount the driver will charge the school system to drive that route. How should the drivers be assigned to the routes to minimize the school system's cost? After you find the optimal assignments, use conditional formatting so that the cost the school system pays for each route is highlighted in red and whenever the cheapest bid is not used for a route, that bid is highlighted in green.

Nick Johnson
Nick Johnson
Numerade Educator

Problem 67

Allied Freight supplies goods to three customers, who each require 30 units. The company has two warehouses. In warehouse 1, 40 units are available, and in warehouse 2,30 units are available. The costs of shipping one unit from each warehouse to each customer are shown in the file $\mathrm{P} 05$ 67.xlsx. There is a penalty for each unsatisfied customer unit of demand-with customer 1 , a penalty cost of $$\$ 90$$ is incurred; with customer $$2, \$ 80$$; and with customer $$3, \$ 110$$.
a. Determine how to minimize the sum of penalty and shipping costs.
b. Use SolverTable to see how a change in the unit penalty $\operatorname{cost}$ of customer 3 affects the optimal cost.
c. Use SolverTable to see how a change in the capacity of warehouse 2 affects the optimal cost.

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06:42

Problem 68

Referring to the previous problem, suppose that Allied Freight can purchase and ship extra units to either warehouse for a total cost of $$\$ 100$$ per unit and that all customer demand must be met. Determine how to minimize the sum of purchasing and shipping costs.

Subham Jyoti Mishra
Subham Jyoti Mishra
Numerade Educator

Problem 69

Based on Glover and Klingman (1977). The government has many computer files that must be merged frequently. For example, consider the Survey of Current Income (SCI) and the Consumer Price Service (CPS) files, which keep track of family income and family size. The breakdown of records in each file is given in the file P05 $69 . x \mathrm{sx}$. SCI and CPS files contain other pieces of data, but the only variables common to the two files are income and family size. Suppose that the SCI and CPS files must be merged to create a file that will be used for an important analysis of government policy. How should the files be merged? We would like to lose as little information as possible in merging the records. For example, merging an SCI record for a family with income $$\$ 25,000$$ and family size 2 with a CPS record for a family with income $$\$ 26,000$$ and family size 2 results in a smaller loss of information than if an $\mathrm{SCI}$ record for a family with income $$\$ 25,000$$ and family size 2 is merged with a CPS record for a family with income $$\$ 29,000$$ and family size 3. Let the "cost" of merging an $\mathrm{SCI}$ record with a CPS record be $\left|I_{\mathrm{SCI}}-I_{\mathrm{CPS}}\right|+\left|F S_{\mathrm{SCI}}-F S_{\mathrm{CPS}}\right|$ where $I_{\mathrm{SCl}}$ and $I_{\mathrm{CPS}}$ are the incomes from the SCI and CPS records, and $F S_{\mathrm{SCI}}$ and $F S_{\mathrm{CPS}}$ are the family sizes. Determine the least expensive way to merge the SCI and CPS records.

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04:58

Problem 70

Based on Evans (1984). Currently, State University can store 200 files on hard disk, 100 files in computer memory, and 300 files on tape. Users want to store 300 word-processing files, 100 packaged-program files, and 100 data files. Each month a typical word processing file is accessed eight times; a typical packaged-program file, four times; and a typical data file, two times. When a file is accessed, the time it takes for the file to be retrieved depends on the type of file and on the storage medium. The times are listed in the file P05_70.xlsx. The goal is to minimize the total time per month that users spend accessing their files. Determine where files should be stored.

Amy Jackson
Amy Jackson
Numerade Educator
01:58

Problem 71

Bloomington has two hospitals. Hospital 1 has four ambulances, and hospital 2 has two ambulances. Ambulance service is deemed adequate if there is only a $10 \%$ chance that no ambulance will be available when an ambulance call is received by a hospital. The average length of an ambulance service call is $20 \mathrm{~min}$ utes. Given this information, queueing theory tells us that hospital 1 can be assigned up to 4.9 calls per hour and that hospital 2 can be assigned up to 1.5 calls per hour. Bloomington has been divided into 12 districts. The average number of calls per hour emanating from each district is given in the file P05_71.xIsx. This file also shows the travel time (in minutes) needed to get from each district to each hospital. The objective is to minimize the average travel time needed to respond to a call. Determine the proper assignment of districts to hospitals. (Hint: Be careful about defining the supply points!)

Sheryl Ezze
Sheryl Ezze
Numerade Educator
01:17

Problem 72

In Problem 55 , assume that before being shipped to Los Angeles or New York, all oil produced at the wells must be refined at either Galveston or Mobile. To refine 1000 barrels of oil costs $$\$ 5780$$ at Mobile and $$\$ 6250$$ at Galveston. Assuming that both Mobile and Galveston have infinite refinery capacity, determine how to minimize the daily cost of transporting and refining the oil requirements of Los Angeles and New York.

Carson Merrill
Carson Merrill
Numerade Educator
00:42

Problem 73

Rework the previous problem under the assumption that Galveston has a refinery capacity of 150,000 barrels per day and Mobile has a refinery capacity of 180,000 barrels per day.

Charles Carter
Charles Carter
Numerade Educator
10:45

Problem 74

Oilco has oil fields in San Diego and Los Angeles. The San Diego field can produce up to 500,000 barrels per day, and the Los Angeles field can produce up to 400,000 barrels per day. Oil is sent from the fields to a refinery, either in Dallas or in Houston. (Assume that each refinery has unlimited capacity.) To refine 1000 barrels costs $$\$ 5700$$ at Dallas and $$\$ 6000$$ at Houston. Refined oil is shipped to customers in Chicago and New York. Chicago customers require 400,000 barrels per day, and New York customers require 300,000 barrels per day. The costs of shipping 100,000 barrels of oil (refined or unrefined) between cities are shown in the file $\mathrm{P} 05_{-} 74$.xIsx.
a. Determine how to minimize the total cost of meeting all demands.
b. If each refinery had a capacity of 380,000 barrels per day, how would you modify the model in part a?

Jacquelyn Trost
Jacquelyn Trost
Numerade Educator
04:53

Problem 75

At present, 500 long-distance calls must be routed from New York to Los Angeles (L.A.), and 400 calls must be routed from Philadelphia to L.A. On route to L.A. from Philadelphia or New York, calls are sent through Indianapolis or Cleveland, then through Dallas or Denver, and finally to L.A. The number of calls that can be routed between any pair of cities is shown in the file P05_75.xlsx. The phone company wants to know how many of the $500+400=900$ calls originating in New York and Philadelphia can be routed to L.A. Set this up as a minimum cost network flow model-that is, specify the nodes, arcs, shipping costs, and arc capacities. Then solve it.

Gio Maya
Gio Maya
Numerade Educator
00:50

Problem 76

Eight students need to be assigned to four dorm rooms at Faber College. Based on "incompatibility measurements," the cost incurred for any pair of students rooming together is shown in the file P05_76.xIsx. How should the students be assigned to the four rooms to minimize the total incompatibility cost?

Elizabeth Xu
Elizabeth Xu
Numerade Educator
05:42

Problem 77

Based on Ravindran (1971). A library must build shelving to shelve 2004 -inch-high books, 100 8-inchhigh books, and 80 12-inch-high books. Each book is 0.5 inch thick. The library has several ways to store the books. For example, an 8-inch-high shelf can be built to store all books of height less than or equal to 8 inches, and a 12 -inch-high shelf can be built for the 12 -inch books. Alternatively, a 12 -inch-high shelf can be built to store all books. The library believes it costs $$\$ 2300$$ to build a shelf and that a cost of $$\$ 5$$ per square inch is incurred for book storage. (Assume that the area required to store a book is given by the height of the storage area multiplied by the book's thickness.) Determine how to shelve the books at minimum cost. (Hint: Create nodes $0,4,8$, and 12 , and make the cost associated with the arc joining nodes $i$ and $j$ equal to the total cost of shelving all books of height greater than $i$ and less than or equal to $j$ on a single shelf.)

Carson Merrill
Carson Merrill
Numerade Educator
01:56

Problem 78

In the original RedBrand problem (Example 5.4), suppose that the company could add up to 100 tons of capacity, in increments of 10 tons, to any single plant. Use SolverTable to determine the yearly savings in cost from having extra capacity at the various plants. Assume that the capacity will cost $$\$ 28,000$$ per ton right now, Also, assume that the annual cost savings from having the extra capacity will extend over 10 years, and that the total 10 -year savings will be discounted at an annual $10 \%$ interest rate. How much extra capacity should the company purchase, and which plant should be expanded?

Carson Merrill
Carson Merrill
Numerade Educator

Problem 79

Based on Jacobs (1954). The Carter Caterer Company must have the following number of clean napkins available at the beginning of each of the next 4 days: day 1,1500 ; day 2,1200 ; day 3,1800 ; day 4,600 . After being used, a napkin can be cleaned by one of two methods: fast service or slow service. Fast service costs 10 cents per napkin, and a napkin cleaned via fast service is available for use the day after it is last used. Slow service costs 6 cents per napkin, and these napkins can be reused 2 days after they are last used. New napkins can be purchased for a cost of 20 cents per napkin. Determine how to minimize the cost of meeting the demand for napkins during the next 4 days. (Note: There are at least two possible modeling approaches, one network and one nonnetwork. See if you can model it each way.)

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06:07

Problem 80

Kellwood, a company that produces a single product, has three plants and four customers. The three plants will produce 3000,5000 , and 5000 units, respectively, during the next time period. Kellwood has made a commitment to sell 4000 units to customer 1 , 3000 units to customer 2 , and at least 3000 units to customer 3 . Both customers 3 and 4 also want to buy as many of the remaining units as possible. The profit associated with shipping a unit from each plant to each customer is given in the file P05_80.xlsx. Determine how to maximize Kellwood's profit.

Goutam Chand
Goutam Chand
Numerade Educator
01:58

Problem 81

I have put four valuable paintings up for sale. Four customers are bidding for the paintings. Customer 1 is willing to buy two paintings, but each other customer is willing to purchase at most one painting. The prices that each customer is willing to pay are given in the file P05 81.xlsx. Determine how to maximize the total revenue received from the sale of the paintings.

Khushbu Rani
Khushbu Rani
Numerade Educator
02:45

Problem 82

Powerhouse produces capacitors at three locations: Los Angeles, Chicago, and New York. Capacitors are shipped from these locations to public utilities in five regions of the country: northeast (NE), northwest (NW), midwest (MW), southeast (SE), and southwest (SW). The cost of producing and shipping a capacitor from each plant to each region of the country is given in the file P05_82.xlsx. Each plant has an annual production capacity of 100,000 capacitors. Each year, each region of the country must receive the following number of capacitors: NE, 55,000; NW, 50,000; MW, 60,$000 ; \mathrm{SE}, 60,000 ;$ SW, 45,000. Powerhouse believes that shipping costs are too high, and it is therefore considering building one or two more production plants. Possible sites are Atlanta and Houston. The costs of producing a capacitor and shipping it to each region of the country are also given in the file P05_82.xIsx. It costs $$\$ 3$$ million (in current dollars) to build a new plant, and operating each plant incurs a fixed cost (in addition to variable shipping and production costs) of $$\$ 50,000$$ per year. A plant at Atlanta or Houston will have the capacity to produce 100,000 capacitors per year. Assume that future demand patterns and production costs will remain unchanged. If costs are discounted at a rate of $12 \%$ per year, how can Powerhouse minimize the net present value (NPV) of all costs associated with meeting current and future demands?

Varsha Aggarwal
Varsha Aggarwal
Numerade Educator
05:37

Problem 83

Based on Hansen and Wendell (1982). During the month of July, Pittsburgh resident Bill Fly must make four round-trip flights between Pittsburgh and Chicago. The dates of the trips are shown in the file P05_83.xIsx. Bill must purchase four round-trip tickets. Without a discounted fare, a round-trip ticket between Pittsburgh and Chicago costs $$\$ 500$$. If Bill's stay in a city includes a weekend, he gets a $20 \%$ discount on the round-trip fare. If his stay is more than 10 days, he receives a $30 \%$ discount, and if his stay in a city is at least 21 days, he receives a $35 \%$ discount. However, at most one discount can be applied toward the purchase of any ticket. Determine how to minimize the total cost of purchasing the four round-trip tickets. (Hint: It might be beneficial to pair one half of one round-trip ticket number with half of another round-trip ticket.)

Cathy Wang
Cathy Wang
Numerade Educator
03:41

Problem 84

Three professors must be assigned to teach six sections of finance. Each professor must teach two sections of finance, and each has ranked the six time periods during which finance is taught, as shown in the file $\mathrm{P} 05$ 84.xlsx. A ranking of 10 means that the professor wants to teach at that time, and a ranking of 1 means that he or she does not want to teach at that time. Determine an assignment of professors to sections that maximizes the total satisfaction of the professors.

N A
N A
Numerade Educator

Problem 85

Based on Denardo et al. (1988). Three fires have just broken out in New York. Fires 1 and 2 each require two fire engines, and fire 3 requires three fire engines. The "cost" of responding to each fire depends on the time at which the fire engines arrive. Let $t_{i j}$ be the time in minutes when the engine $j$ arrives at fire $i$ (if it is dispatched to that location). Then the cost of responding to each fire is as follows: fire $1,6 t_{11}+4 t_{12}$; fire 2 , $7 t_{21}+3 t_{22}$; fire $3,9 t_{31}+8 t_{32}+5 t_{33}$. There are three fire companies that can respond to the three fires. Company 1 has three engines available, and companies 2 and 3 each have two engines available. The time (in minutes) it takes an engine to travel from each company to each fire is shown in the file P05_85.xlsx.
a. Determine how to minimize the cost associated with assigning the fire engines. (Hint: A network with seven destination nodes is necessary.)
b. Would the formulation in part a still be valid if the cost of fire 1 were $4 t_{11}+6 t_{12}$ ?

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Problem 86

A company produces several products at several different plants. The products are then shipped to two warehouses for storage and are finally shipped to one of many customers. How would you use a network flow model to help the company reduce its production and distribution costs? Pay particular attention to discussing the data you would need to implement a network flow model.

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Problem 87

You want to start a campus business to match compatible male and female students for dating. How would you use the models in this chapter to help you run your business?

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Problem 88

You have been assigned to ensure that each high school in the Indianapolis area is racially balanced. Explain how you would use a network model to help attain this goal.

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00:38

Problem 89

In the crew-scheduling model in Example 5.7, there are only two cities. Suppose there are more than two cities. Is it possible to modify the network approach appropriately? Discuss how you would do it.

Sneha Ravi
Sneha Ravi
Numerade Educator