Matching Supply with Demand An Introduction to Operations Management 4th Edition By Gerard Cachon – Test Bank

Chapter 11 Scheduling to Prioritize Demand

1) When working with any scheduling system, what is the common objective across operations?

Answer: Matching demand to resources.
Explanation: The scheduler needs to consider when a particular resource will be used to process the demand. Scheduling can span across a variety of time ranges (long, medium, and short). Resources and time demands vary across many operations such as manufacturing, transportation, and patient scheduling. The goal for any operation that involves scheduling is to make sure that the resources are utilized as much as possible and that demand is served within a reasonable amount of time.
Difficulty: 3 Hard
Topic: Scheduling Timeline and Applications
AACSB: Analytical Thinking
Blooms: Analyze

2) Aurelina Hair Salon has a busy morning ahead of them. During the first 3 hours of the day, their top hair stylist, Marcos, has 9 clients to serve. What is the flow rate in clients per minute that Marcos has to serve?

Answer: .05 jobs per minute.
Explanation: To figure out the flow rate (R) we need to divide the inventory (I) by the flow time (T) or (R = I/T).
The first 3 hours of the day is equivalent to 180 minutes (3 * 60 = 180). If Marcos serves 9 clients during this time, then you calculate 9/180 = .05 jobs per minute.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply

[The following information applies to questions 3-6.]

Qi at Sun City Title Company
Qi is an underwriter who works at Sun City Title Company where she processes loans daily. She usually takes an average of 40 minutes to process each loan or job and can identify how long each one will take based on a few key indicators within the application. Today, she has five loans that she must process by the end of the day. Each job is labeled in alphabetical order based on the order in which it arrived. For example, A arrived first, and B came in second, etc. (See table below)

Job A B C D E F
Processing Time (minutes) 50 40 60 30 25 35

3) Qi’s colleague suggests that she work through each job in a first-come-first-served (FCFS) sequence. Why would this not be the best method to use in this situation?

Answer: FCFS doesn’t take into consideration the varying process times which leads to long flow times.
Explanation: Each job has a different set of circumstances that complicate the length of time to process it. Although FCFS may seem like the quickest way to get started and work through each job, rearranging the order can organize a flow to these jobs in a more time-efficient way.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Analytical Thinking
Blooms: Analyze

4) Let’s say, Qi’s office requires underwriters to follow the shortest-processing-time (SPT) rule. In what order will Qi complete the jobs with SPT?
A) A, B, C, D, E, F
B) E, D, F, B, A, C
C) C, D, E on Day 1 and A, B, F on Day 2
D) D, E, F on Day 1 and A, B, C on Day 2
E) C, A, B, F, D, E

Answer: B
Explanation: With SPT or shortest-processing-time, jobs are performed in an order that is based on the amount of time each one takes to complete. The quickest job is undertaken first, while the longest job is saved for last. In Qi’s case, Job E should be the first one she works on because it is a 25-minute process. She will then work on Job D for 30 minutes, Job F for 35 minutes, and so on. Her last job for today should be Job C because it will take a full hour to complete.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply

5) Let’s say Qi decided not to waste a minute of her day and immediately starts the jobs according to the FCFS rule. What would the average flow time be after these five jobs?
A) 910
B) 160
C) 162
D) 150
E) 152

Answer: E
Explanation: Looking at the chart, FCFS means that jobs are completed in the order in which they arrive: A, B, C, D, E, F. Job A has a flow time equal to its processing time of 45 minutes. Job B has a 90-minute flow time (45 minutes waiting for A plus 50 minutes for its own processing time). Job C has a flow time of 150 minutes (90 minutes waiting and 60 minutes for processing). Job D has a flow time of 180 minutes (150 minutes waiting plus 30 minutes to process). Job E has a flow time of 205 minutes (180 minutes waiting plus 25 minutes to process). Finally, Job F has a flow time of 240 minutes (205 minutes waiting plus 35 minutes to process). The average flow time of all six jobs is calculated by 45 + 90 + 150 + 180 + 205 + 240 = 910/6 = 151.67 = 152.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply

6) Before starting her work, Qi decides to take a moment to calculate average flow times. After she learns that the average flow time under FCFS is 152 minutes, she predicts that the SPT rule must yield a shorter average flow time. Is she correct?

Answer: Yes.
Explanation: SPT, or shortest-processing-time, would have the job order of E, D, F, B, A, C. Let’s calculate the SPT average flow time to determine if it would be less than 152 minutes. The flow time (and processing time) for E is 25 minutes. Job D has a flow time of 55 minutes (25 minutes of waiting plus 30 minutes to process). Job F has a flow time of 90 minutes (55 minutes waiting plus 35 minutes to process). Job B has a flow time of 130 minutes (90 minutes waiting plus 40 minutes to process). Job A has a flow time of 180 minutes (130 minutes waiting plus 50 minutes to process). Job C has a flow time of 240 minutes (180 minutes waiting plus 60 minutes to process). The average flow time is calculated by 25 + 55 + 90 + 130 + 180 + 240 = 720/6 = 120. The average flow time under FCFS (above) was 152 minutes. Thus, 152 – 120 = 32, so SPT is 32 minutes less than the average flow time of FCFS.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Analytical Thinking
Blooms: Analyze

7) Brianna is a software developer who has four programs to complete this season. She estimates that one program will take two weeks to complete, two of them will take three weeks to complete and the other one will take her four weeks. Brianna plans to use some of her vacation time this season, so she will not accept any more program requests beyond these four this season.

What is Brianna’s flow rate, or projects per week, during the time these programs are worked on?

Answer: .33.
Explanation: Flow rate (R) is determined by R = I/T. I represents inventory and T is for flow time. Brianna has 4 jobs to complete within 12 weeks (2 + 3 + 3 + 4 = 12). Calculate 4/12 = .33 flow rate.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Analyze

[The following information applies to questions 8-10.]

Last season, Brianna had one of the busiest periods of her career in software development. Take a look at the table below to see the number of programs she agreed to build. Once Brianna accepts a collection of jobs, or programs to build, at the beginning of a season, she does not accept any more until the next season. Brianna utilizes the shortest-processing-time (SPT) scheduling application.

Job (programs to build) A B C D E F
Processing time (weeks) 2 1 4 6 3 5

8) Recall that Brianna uses the SPT rule. In what sequence did she build these six programs?

Answer: B, A, E, C, F, D.
Explanation: When using shortest-processing-time (SPT), jobs are completed according to the length of time they take. In other words, SPT begins with the quickest job and ends with the one that will consume the most amount of time.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply

9) What was Brianna’s flow time of job F? (Enter your answer in weeks).

Answer: 15 weeks.
Explanation: Recall that flow time is the sum of the wait time plus the process time. Job B had a flow time of 1 week. Job A was 3 weeks (1 waiting and 2 for processing). Job E took 6 weeks (3 weeks waiting and 3 weeks of processing). Job C was 10 weeks (6 weeks waiting and 4 weeks to process). Finally, Job F had a flow time of 15 weeks (10 weeks waiting and 5 weeks to process). In this situation, we do not look at Job D because it was worked after job F under the SPT rule.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply

10) What was Brianna’s average flow time of jobs in the system?

Answer: 9.33.
Explanation: Let’s continue with the calculations above and figure out the flow time for the last job that Brianna undertook according to the SPT rule, Job D. Job D waited 15 weeks and then required 6 more weeks of its own processing time, which is a total of 21 weeks. To understand the average flow time, we need to add the flow time of all her jobs and divide the total by 6.
Hence, 1 + 3 + 6 + 10 + 15 + 21 = 56/6 = 9.33. Brianna’s average flow time of jobs in the system was 9.33 weeks.
Difficulty: 3 Hard
Topic: Resource Scheduling-Shortest Processing Time
AACSB: Knowledge Application
Blooms: Apply