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9. Mike Reynolds has four assignments due in class tomorrow, and his class
times are as follows.
Class Time
Each class lasts one hour, and Mike has no other classes. It is now midnight,
Job Processing time Due date
——— ———————– ———
Using earliest due date (EDD) rule:
Using shortest processing time (SPT) rule:
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10.* Eight jobs have arrived in the following order:
Job
Processing
Time
Due
Date
17 21
23 7
35 8
42 5
56 17
69 16
714 38
84 12
Find and compare the average flowtime, lateness, and tardiness for the
following sequencing rules:
Arrival order:
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SPT:
EDD:
11.* In this chapter we noted that the EDD rule minimizes the maximum job
tardiness and maximum lateness while the SPT rule minimizes the average
flowtime. However, neither of these rules minimize the average lateness or
average tardiness. Use the data in problem 10 to do the following:
a. Try to find a sequence that minimizes the average lateness.
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From Problem #10 we know the following:
This question can be addressed by experimentation using the Sequencing
spreadsheet template. This can be used as a competitive exercise among
12. Monday morning Baxter Industries has the following jobs waiting for
processing in two departments, milling and drilling, in that order.
Time Required (hours)
Job Mill Drill
Develop a minimum makespan schedule using Johnson’s rule.
13. Graph the minimum makespan schedule in Problem 12 on a Gantt chart.
MILL
DRILL
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Makespan = 47 hours (notice that when all jobs finish on the mill, they can
14. Dan’s Auto Detailing business performs two major activities: exterior
cleanup, and interior detailing. Based on the size of car and condition,
time estimates for six cars on Monday morning are as shown in the
accompanying table.
Car Number
1 2 3 4 5 6
Sequence the cars so that all exterior detailing is done first and total
Since it is a 2-facility, n-job problem, we use Johnson’s rule. The processing times are:
Job Exterior Interior
— ——– ——–
Using Johnson’s rule, we generate the following sequence:
15. Draw a Gantt chart of your solution to Problem 14. Evaluate the idle time, if
any, for these two resources—exterior and interior cleaning capability.
The schedules are shown on the following Gantt charts (timelines are not to scale).
Exterior:
|—-|——-|——-|——-|——|———|
Interior (double lines indicate idle time):
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|—–|===|—–|===|——-|——|===|——|===|——|
Even for a relatively simple problem structure like this, Johnson’s rule is
Case Teaching Notes: Balloons Aloha
Overview
A small business must sequence jobs using a single resource helium tank to fill
balloons used in parties, wedding, bachelor parties, etc. Processing and due date
times are given and the assistant store manager, Mr. Lee Sailboat, wants to use the
sequential order 1, 2, 3, 4, 5, and 6. Customer # 5 is their top customer. Since
balloons lose air quickly they wait to the last minute to fill the balloons. They are
growing at 15% per year!
Case Questions for Discussion
1. Compute the average flowtime, lateness, and tardiness for this group of jobs
using Mr. Sailboat’s sequential order of 1 (first), 2, 3, 4, 5, and 6 (last).
2. In what order would the jobs be processed using the SPT rule? Compute the
average flowtime, lateness, and tardiness for this group of jobs.
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3. Compare the answers in questions 1 and 2.
SPT minimizes the average time a job spends in the shop either waiting or being
processed (average flow time of 461.67 versus 588.33). Even though the
4. What are your short-term recommendations for this set of six jobs? Justify and
explain.
Use SPT to sequence these jobs. Ms. Davis may want to bring in some
part-time help to ensure all work is done in time for the special occasions but
5. What are your long-term recommendations with respect to sequencing jobs at
Balloons Aloha? Justify and explain.
They need to evaluate equipment capacity and determine “when” they need to
install a second helium tank of the same size, one larger tank with multiple
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