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This example demonstrates how to use linear programming to determine the optimal production quantities of energy and refresher drinks, based on ingredient constraints and profit margins.
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Linear Programming : Introductory Example THE PROBLEM A factory produces two types of drink, an ‘energy’ drink and a ‘refresher’ drink. The day’s output is to be planned. Each drink requires syrup, vitamin supplement and concentrated flavouring, as shown in the table. The last row in the table shows how much of each ingredient is available for the day’s production. How can the factory manager decide how much of each drink to make?
THE PROBLEM Energy drink sells at £1 per litre Refresher drink sells at 80 p per litre
FORMULATION Syrup constraint: Let x represent number of litres of energy drink Let y represent number of litres of refresher drink 0.25x + 0.25y 250 x + y 1000
FORMULATION Vitamin supplement constraint: Let x represent number of litres of energy drink Let y represent number of litres of refresher drink 0.4x + 0.2y 300 2x + y 1500
FORMULATION Concentrated flavouring constraint: Let x represent number of litres of energy drink Let y represent number of litres of refresher drink 6x + 4y 4800 3x + 2y 2400
FORMULATION • Objective function: • Let x represent number of litres of energy drink • Energy drink sells for £1 per litre • Let y represent number of litres of refresher drink • Refresher drink sells for 80 pence per litre • Maximise x + 0.8y
SOLUTION Empty grid to accommodate the 3 inequalities
SOLUTION 1st constraint Draw boundary line: x + y = 1000
SOLUTION 1st constraint Shade out unwanted region: x + y 1000
SOLUTION Empty grid to accommodate the 3 inequalities
SOLUTION 2nd constraint Draw boundary line: 2x + y = 1500
SOLUTION 2nd constraint Shade out unwanted region: 2x+ y 1500
SOLUTION Empty grid to accommodate the 3 inequalities
SOLUTION 3rd constraint Draw boundary line: 3x + 2y = 2400
SOLUTION 3rd constraint Shade out unwanted region: 3x + 2y 2400
SOLUTION All three constraints: First: x + y 1000
SOLUTION All three constraints: First: x + y 1000 Second: 2x + y 1500
SOLUTION All three constraints: First: x + y 1000 Second: 2x + y 1500 Third: 3x + 2y 2400
SOLUTION All three constraints: First: x + y 1000 Second: 2x + y 1500 Third: 3x + 2y 2400 Adding: x 0 and y 0
SOLUTION Feasible region is the unshaded area and satisfies: x + y 1000 2x + y 1500 3x + 2y 2400 x 0 and y 0
SOLUTION Evaluate the objective function x + 0.8y at vertices of the feasible region: O: 0 + 0 = 0 A: 0 + 0.8x1000 = 800 B: 400 + 0.8x600 = 880 C: 600 + 0.8x300 = 840 D: 750 + 0 = 750 A B C D O Maximum income = £800 at (400, 600)