LINEAR PROGRAMMING
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Miscellaneous Examples Example 9 (Diet problem) A dietician has to develop a special diet using two foods P and Q. Each packet (containing 30 g) of food P contains 12 units of calcium, 4 units of iron, 6 units of cholesterol and 6 units of vitamin A. Each packet of the same quantity of food Q contains 3 units of calcium, 20 units of iron, 4 units of cholesterol and 3 units of vitamin A. The diet requires atleast 240 units of calcium, atleast 460 units of iron and at most 300 units of cholesterol. How many packets of each food should be used to minimise the amount of vitamin A in the diet? What is the minimum amount of vitamin A? Solution Let x and y be the number of packets of food P and Q respectively. Obviously x ≥ 0, y ≥ 0. Mathematical formulation of the given problem is as follows: Minimise Z = 6x + 3y (vitamin A) subject to the constraints 12x + 3y ≥ 240 (constraint on calcium), i.e.
4x + y ≥ 80
... (1)
4x + 20y ≥ 460 (constraint on iron), i.e.
x + 5y ≥ 115
... (2)
6x + 4y ≤ 300 (constraint on cholesterol), i.e. 3x + 2y ≤ 150
... (3)
x ≥ 0, y ≥ 0
... (4)
Let us graph the inequalities (1) to (4). The feasible region (shaded) determined by the constraints (1) to (4) is shown in Fig 12.10 and note that it is bounded.
Fig 12.10