Question 1 (10 marks)
A landscaper wants to mix her own fertilizer containing a minimum of 50 units of phosphates,
240 units of nitrates and 210 units of calcium. Brand 1 contains 1 unit of phosphates, 6 units of
nitrates and 15 units of calcium. Brand 2 contains 5 units of phosphates, 8 units of nitrates and
6 units of calcium. Brand 1 costs $250 per kilogramme; brand 2 costs $500 per kilogramme.
Model this information into a linear programming problem. Declare your variables
unambiguously and name the constraints. DO NO SOLVE.
(10)
Question 2 (13 marks)
Solve the following minimization problem graphically. Use a scale of 1cm to 25 units on the x-axis
and a scale of 1cm to 5 units on the y-axis.
(13)
Minimize C = 20x+ 30y
Subject to 9x+ l00y 4500
3x+ 20y::;; 1200
15000::; 75x + 200 y
y::;; 60
X; y ~0
Question 3 (29 marks)
Consider the following L-P model:
Minimize Z = 240x+I20y
Subject to 4x + 8y 56
2x+2y~24
3x+ y 18
x~0;y~0
3.1 Write down the dual of the model.
(5)
3.2 Solve the dual model.
{14)
3.3 Suppose the solution of the dual model is a= 0 ; b = 30 ; c = 60 ; 11 = O ; 12 = 0 ; D = 1800.
Use this solution to determine the solution ofthe given primal model.
(10)
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