THE UNIVERSITY OF HONG KONG
B.ENG. EXAMINATIONS
DEPARTMENT OF INDUSTRIAL ENGINEERING AND MANUFACTURING SYSTEMS ENGINEERING
(IMSE3136) OPERATIONS PLANNING AND CONTROL
December 14, 2022
9:30 am — 12:30 pm
Answer ALL NINE questions.
Instructions:
e
e
e
Please write down your answers in the answer book.
You may use the graph papers to answer some of the questions.
For numerical calculations, please write all the steps clearly to justify your answers. Please also
correct all the numerical values in your steps, if not exact, to 4 decimal places.
Use of Calculators:
“Only approved calculators as announced by the Examinations Secretary can be used in this examination.
It is candidates’ responsibility to ensure that their calculator operates satisfactorily, and candidates must
record the name and type of the calculator used on the front page of the examination script.”
(IMSE3136 — page 1 of 6)
Question |
Suppose that you are a general manager of a subsidiary of a global fast-food restaurant based in the United
States. Currently, the subsidiary uses local suppliers to supply the ingredients, materials, and all required
items to enable their business. More recently, you have been consulted by the headquarters in the United
States to consider centralized purchasing approaches (i.e., the headquarters will manage all the sourcing
and procurement activities for all the subsidiaries around the globe). What are the pros and cons of
centralized and decentralized purchasing approaches? What factors would you consider when deciding
which approach to adopt?
(10 marks)
Question 2
Airline A’s strategy seems to leverage its medium-size airplanes’ characteristics: flying into smaller and
non-hub airports. On the other hand, Airline B operates more flight routes with larger-size airplanes
between hub airports. When considering the prices of flight tickets, the prices of Airline B’s flight routes
per mile are typically lower. What strategies do the two airlines adopt? What are the pros and cons?
(8 marks)
Question 3
Periodic systems and perpetual (continuous review) systems are two popular classes of inventory counting
systems. Please provide a real-life example of each of the systems, and discuss their pros and cons.
(12 marks)
Question 4
Consider the following forecast and actual demands of 24 periods.
Period
Forecast demand
Actual demand
]
80
83
2
87
89
3
92
93
Period
Forecast demand
Actual demand
13
88
90
14
92;
92}
15
102;
104)
4
3
88 | 103;
87}
103}
lo;
100;
102;
17}
105;
108;
6
80;
79)
7
89}
88}
8
9;
93|110;}
95)113]
10;
105]
108}
Il}
113}
115]
12
93
93
18)
88);
91}
19];
93)
96}
20};
87)
89}
22}
120]
123}
23)
110}
112|
24
93
96
21}
123)
124)
(a)
Please plot a control chart with 2s limits. Use data from the first twelve periods to develop the
control chart, and then evaluate the remaining data with the control chart.
(5 marks)
(b)
Using the result from Question 4a, can you conclude that there 1s no bias in the forecast?
(3 marks)
(IMSE3136 — page 2 of 6)
Question 5
A processing facility supplies chemical IMSE3136 to its factories for production purposes. The chemical
IMSE3136 is continuously transported from the processing facility to the final destinations through
pipelines. The total demand for IMSE3136 from all the factories is 25,000L per day. All the factories
operate 365 a year. On the other hand, the processing facility can produce 150,000L per day. However,
the manager of the processing facility found out that 5,000L of IMSE3136 is constantly lost per day during
transportation due to certain damage to the pipeline infrastructure. Given that the carrying cost is $50/L
per year, and the setup cost for a production run of IMSE3136 is $10,000. The processing facility aims to
minimize the total cost of supplying the chemical.
(a)
What is the optimal production volume of IMSE3136 each time the processing facility produces
it?
(5 marks)
(b)
What is the total annual cost?
(5 marks)
(c)
What is the cycle time for the optimal run size?
(5 marks)
Question 6
Two 24-hour restaurants — IMSE and IELM — both order a kind of soda from the same supplier. IMSE
adopts a perpetual ordering system (i.e., a continuous review system). Whenever the volume of the soda
on hand is lower than the reorder point (ROP), IMSE would immediately place an order. On the contrary,
IELM adopts a periodic ordering system and places an order of the soda at the end of every Wednesday
(i.e., 23:59). Upon any request from IMSE and JELM, the supplier will deliver the order in exactly one
day. Given that daily demands (in liter) for the soda at IMSE and IELM, denoted as djysg and dj¢,y,
both follow the same probability distribution function independently: djysg~N(30,37) and
dimsg~N (30,37). In other words, the daily demands for the soda at IMSE and IELM are both normally
distributed with a mean of 30 L and a standard deviation of 3L. Suppose that it is now December 14 (Wed)
23:59 and the volumes of soda at IMSE and IELM are 230L and 160L, respectively.
(a)
(b)
(c)
What is the ROP the restaurant IMSE shall adopt to ensure the desired service level of 95%?
(5 marks)
| What volume of soda should IELM order to ensure the desired service level of 95%’?
(5 marks)
After IELM places an order just right now, what is the probability that IMSE orders earlier than
IELM does?
(10 marks)
(IMSE3136 — page 3 of 6)
Question 7
B
C
D
E
14
18
20
17
18
bh
14
15
19
16
17
WB
I2
16
15
14
17
&
Il
13
14
12
14
10
16
15
14
13
=
A
nA
A food delivery company has just received five orders (Orders 1 to 5) for delivery and identified five
riders (Riders A to E) available to dispatch. Their information system has calculated the estimated delivery
times (in minutes) of the orders by the different riders based on their current locations, as shown below.
Rider
Order
The system also indicates that the customer who placed order 2 wrote a complaint related to rider D two
months ago, such that the rider is unable to take order 2.
(a)
The system aims to minimize the total estimated delivery time. What is the optimal allocation of
(5 marks)
riders to orders?
(b)
Rider A has just reported to the service center that his motorcycle has some minor issues to fix.
He will probably need to take 5 to 10 minutes to fix the motorcycle at the current location. How
will you allocate the riders to the orders, if no further riders are available and the same objective
(5 marks)
in Question 7a still applies?
(IMSE3136 — page 4 of 6)
Question 8
The manager of the factory needs to assign seven tasks, with times and precedence relationships as shown
in the following table, to workstations. She aims to achieve an output of 24 units per eight-hour day.
Task | Duration (minutes) | Immediate Predecessor
A
2
B
4
A
C
4
D
2
B
E
12
C
F
12
D
G
10
E,F
(a)
Draw the precedence diagram.
(2 marks)
(b)
What is the cycle time?
(1 mark)
(c)
What is the theoretical minimum number of stations?
(1 mark)
(d)
Assign tasks to workstations by the rule of most following tasks, and use the rule of shortest
processing time as a tiebreaker. If there is still a tie, you may assume indifference in choice.
(4 marks)
(e)
What is the percentage idle time based on your assignment in Question 8d?
(1 mark)
(IMSE3136 — page 5 of 6)
Question 9
Consider the following product structure tree and the inventory records. It is known that there is a planned
order release for component D = 640 units in week 2, and 180 units of A are needed in week 6.
A
C
D (4)
Component
A
B
C
D
已
B
C
Lead Time (weeks)
]
2
]
Z
]
On-Hand
0
0
60
0
200
Please work out a material requirements plan.
Lot Size
Lot-for-Lot
Lot-For-Lot
120
Lot-For-Lot
Lot-For-Lot
(8 marks)
— End of Paper —
(IMSE3136 — page 6 of 6)