EQC7013: Operations Research Methods
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EQC7013: Operations Research Methods
Semester 1 2020/2021
Question 1 – 5 Marks
i) Department 3 has 2500 hours. Transfers are allowed to departments 2 and 4, and from departments 1 and 2. If Ai measures the labor hours allocated to department i and Tij the hours transferred from department i to department j, then
a. T13 + T23 − T32 − T34 − A3 = 2500
b. T31 + T32 − T23 − T43 + A3 = 2500
c. A3 + T13 + T23 − T32 − T34 = 2500
d. A3 − T13 − T23 + T32 + T34 = 2500
ii) Let M be the number of units to make and B be the number of units to buy. If it costs $2 to make a unit and $3 to buy a unit and 4000 units are needed, the objective function is
a. Max 2M + 3B
b. Min 4000 (M + B)
c. Max 8000M + 12000B
d. Min 2M + 3B
iii) Using minutes as the unit of measurement on the left-hand side of a constraint and using hours on the right-hand side is acceptable since both are a measure of time.
a. True
b. False
iv) If a real-world problem is correctly formulated, it is not possible to have alternative optimal solutions.
a. True
b. False
v) If an LP problem is not correctly formulated, the computer software will indicate it is infeasible when trying to solve it.
a. True
b. False
Question 2 – 8 Marks
A Linear Programming model has been developed below. Its solution will show how many ofthe different type of shoes should be stocked in order to maximize profit. The four constraints measure the storage space in units, special packaging needs, demand and promotion budget, respectively. Assuming that all stocks will be sold.
Let: X1 = Number of Shoe 1
X2 = Number of Shoe 2
X3 = Number of Shoe 3
X4 = Number of Shoe 4
Objective function: 4 X1 + 6 X2 + 5 X3 +3.5 X4
Subject to:
1) 2 X1 + 3 X2 + 3 X3 + X4 <= 120
2) 1.5 X1 + 2 X2 <= 54
3) 2 X2 + X3 + X4 <= 72
4) X2 + X3 >= 12
Xi >= 0
Run the model in Solver and answer the following questions based on the Sensitivity Report:
a) What is the optimal solution? What is the total profit?
b) How many special packaging are needed?
c) Explain how much the profit on Shoe 1 can change before the solution would change.
d) Explain the value of shadow price of storage space and promotion budget, respectively.
e) Would you agree with your colleagues to spend on advertisement with a total cost of $20 if demand can be increased to 86? Why or why not?
Question 3 – 7 Marks
ABC company is producing various clothing for men, women and children. Their Footwear Department is trying to decide what mix of three types of socks to produce. Each full-time employee of the department works 40 hours per week; and the number of full-time employees can never drop below 20. Each part-time worker works 20 hours per week, and there must be at least 2 full-time employees for each part-time employee. The company receives 5,000 feet ofthe material each week. The company would like to produce at least 400 pairs of Children’s socks. The material requirements and labor requirements, along with the revenue per sock sold is given in the following table.
Socks |
Material (feet) |
Labor (in Minutes) |
Revenue (RM, per pair) |
Children |
1 |
40 |
6 |
Women |
1.5 |
45 |
10 |
Men |
2 |
30 |
8 |
Each full-time employee earns RM13 per hour, while each part-time employee earns RM10 per hour. While trying to maximise the profit, the company would like to know
1) How many socks to produce for each type per week.
2) How many full-time and part-time workers should the company employed? Assuming partial employment is possible.
3) Do you think the company should specify the production of Children’s socks? Why or why not?
Define your decision variables, write the model and solve the problem.
(Assuming that partial production and/or partial employees’ hours are allowable)
Question 4 – 5 Marks
Formulate a linear programming model for the following problem. Write the model in Excel (DO NOT have to run Solver)
A bakery is trying a new recipe. They intend to bake a new cake following some nutritional values. The total calories of the cake should be between 300 to 400 calories. Calories from fat should not exceed 20 percent of the total calories. They aim to have at least 50mg of vitamin content and 15mg of mineral content. To ensure its flavor, there must be at least 2 grams of flavoring for each gram of sugar. Some information about each of these ingredients is given below.
Ingredient |
Cost (cent/gram) |
Calories from Fat (per gram) |
Total Calories (per gram) |
Vitamin Content (mg/per gram) |
Mineral Content (mg/per gram) |
Flavoring |
6 |
1 |
3.5 |
1.5 |
1 |
Milk |
13 |
6 5 |
8 |
2 |
1.5 |
Supplement |
15 |
0 |
0 |
4 |
5 |
Sugar |
21 |
0 |
10 |
0 |
0 |
Food agent |
8 |
2 5 |
6 |
1 |
3 |
2021-12-28