Oshimiri Nigeria Limited, a company based in Aba, produces two grades of industrial vanish. The selling price and associated unit variable costs for vanish Grade A and Grade B are shown below: Particulars Grade A Grade B N N Selling Price 2,100 1,500 Material x - N240 per kg 480 240 Skilled Labour - N144 per Hour 720 288 Unskilled Labour - N60 per hour 120 180 Variable overhead - N84 per machine hour 168 336 The fixed overhead costs are N2,600,000 per month. The company plans to maximise profits. The availability of resources for the following month is as follows: Material X 25,000Kg Skilled labour 48,000 hours Unskilled labour 39,000 hours Machine hours 50,000 hours Required:
Identify the objective function and the constraints of the model to be used in determining the optimum production plan for the following month.
Determine the optimum production plan for the month and the associated Profit.
Explain the concept and significance of dual prices and slack variables in the context of the model used by the company in this scenario.
Calculate the dual prices for constraints identified in this scenario. (10 Marks) 58
Suggest ways in which the management can overcome the capacity constraints identified above during the month and the cost implications.
Revise this question
Limiting factors: allocating a single scarce resource › LayoutsLinear programming: formulation and graphical solution › LayoutsLinear programming: slack and shadow prices › Finding slack and shadow pricesSuggested answer
a. Identify the objective function and the constraints of the model (linear programming model) Contribution per unit A B Selling Price N2,100 N1,500 Less Variable costs: Material X 480 240 Labour 1-Skilled 720 288 Labour 2-Unskilled 120 180 Variable overhead 168 336 Total variable cost 1,488 1,044 Unit contribution 612 456 Objective function = C = 612a + 456b Constraints:’ Material will be 2a + b ≤ 25,000 Skilled labour will be 5a + 2b ≤ 48,000 Unskilled labour will be 2a + 3b ≤ 39,000 Machine hours will be 2a + 4b ≤ 50,000 Non negativity a, b ≥ 0 In determining where the constraint equation lines cross a and b axes Material: 2a + b = 25000 Which is a = 12,500 b = 0; a = 0 b = 25,000 Skilled labour: 5a + 2b = 48000 Which is a = 9600 b = o; a = 0 b = 24,000 Unskilled labour: 2a + 3b = 39000 which is a = 19500 b = 0; a = 0 b = 13,000 Machine hours: 2a + 4b = 50000 which is a = 25000 b = 0; a = 0 b = 12,500 Graphically: b Machine hours Material A Unskilled B Skilled C 0 D a The binding constraints are skilled and unskilled labour. 68 From the Graph, the non-limiting factors are material and machine hours while the limiting factors are skilled labour and unskilled labour.
b. Determine the optimum production plan for the month and associated Profit Hence the equations from the linear programme are: Skilled Labour = 5a + 2b = 48,000 …………. …... Equation 1 Unskilled Labour = 2a + 3b = 39,000 ….…….......... Equation 2 Multiply Equation 1 by 3 = 15a + 6b =144,000 …........ Equation 3 Multiply Equation 2 by 2 = 4a + 6b = 78,000 ……….….Equation 4 Subtract Equation 4 from Equation 3 11a = 66,000 a = 6000 Substitute for a in Equation 1 5a + 2b = 48000 5 (6000) + 2b = 48000 30000 + 2b = 48,000 2b = 48000 - 30000 = 18000 b = 9000 Maximum contribution = 612a + 456b = 612 x 6000 + 456 x 9000 = N7,776,000 Less Fixed cost N2,600,000 Net Profit N5,176,000
c. Concept of dual prices and slack variables The concept or model used in this situation of dual or double limiting factor decision tool is linear programming approach and it provides instrument for computing optimum solutions when dual constraints are identified. In this case, some constraints are not limiting while some are limiting. Skilled and unskilled labour hours are the relevant constraints. The dual prices are also known as shadow prices. The shadow or dual price of a constraint is the change in the objective function that is brought about if such constraint is changed by one unit. Slack variables on the other hand refer to the amount of the available resources not used in the optimal solution. Only non limiting resources
d. Calculate the dual prices for constraints identified in this scenario Dual price for Skilled Labour Skilled Labour = 5a + 2b = 48,001 ….…….……..... Equation 1 Unskilled Labour = 2a + 3b = 39,000 ……….……...…Equation 2 Multiply Equation 1 by 3 = 15a + 6b =144,003 …….. Equation 3 Multiply Equation 2 by 2 = 4a + 6b = 78,000 …..…....Equation 4 Subtract Equation 4 from Equation 3 11a = 66,003 a = 6000.2727 Substitute for a in equation 1 2a + 3b = 39,000 2(6,000.2727) + 3b = 39,000 12,000.545 + 3b = 39,000 3b = 39,000 – 12,000.545 = 26,999.4545 b = 8,999.82 New Max. contribution = 612a + 456b = 612 x 6,000.2727 + 456 x 8,999.82 = N7,775,918.14 Old contribution = N7,776,000.00 Dual price for skilled labour = N81.86 Dual price for unskilled labour Skilled Labour = 5a + 2b = 48,000 ……………...Equation 1 Unskilled Labour = 2a + 3b = 39,001 …..……….….Equation 2 Multiply Equation 1 by 3 = 15a + 6b = 144,000 …….... Equation 3 Multiply Equation 2 by 2 = 4a + 6b = 78,002 …….…... Equation 4 Subtract Equation 4 from Equation 3 11a = 65,998 a = 5,999.82 Substitute for a in equation 1 5a + 2b = 48,000 5(5,999.82) + 2b = 48,000 29,999.10 + 2b = 48,000 2b = 48,000 – 29,999.10 = 18,000.90 b = 9,000.45 New maximum contribution = 612a + 456b = 612 x 5,999.82 + 456 x 9,000.45= N7,776,095.04 Old contribution = N7,776,000.00 Dual price for unskilled labour = N95.04 70
e. Ways linear programming model can be used to overcome capacity constraints:
• Investigate alternative sources of materials, skilled labour and unskilled labour. Such sources may necessitate overtime hours and bonuses;
• Increase operating hours of machinery. Including maintenance cost or purchase cost;
• Increase output per machine hours which could lead to additional labour cost;
• Acquisition of machines requiring purchase and capital costs (Investment or capital outlay); and
• Subcontract some of the production to outsiders at higher purchase price which could be higher than the incremental costs.
Examiner’s report Question one is a compulsory question. This question tested candidates understanding of Linear Programming in capacity decision making and dual pricing in situation where there are limiting and non-limiting equations. Being a compulsory question, most candidates attempted this question. However performance was average. Major Pitfall was candidates’ inability to decipher limiting and non-limiting equations as well as computation of dual prices. Candidates are encouraged to intensively use the ICAN study guide when preparing for future ICAN Examinations.
Marking guide Marks Marks
a. Identification of objective function and constraints of the model (30 ticks = 5 marks) 5
b. Determine optimum plan and associated profit. (20 ticks = 5 marks) 5
c. Explain the concept and significance of dual prices and slack variables. Dual price: (Any 4 Points = 2 marks) Slack variables: (Any 4 points = 2 marks) 2 2 4
d. Calculate the dual prices for the constraints. (30 ticks = 10marks) 10
e. Suggest the ways in which the model will be used to overcome capacity constraints. (3 points @ 2 marks each) 6 Total 30 71