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Mathematics and Statistics · Ch 14 — Linear Programming

Maximisation and Minimisation Applications

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Maximisation and Minimisation Applications

The corner-point method turns real commercial questions into a short, repeatable calculation. Two families of problem recur throughout the Std XII (Commerce) course.

Maximisation (profit / output)

Here the objective is a profit or revenue to be made as large as possible, and the constraints are resource ceilings (≤\le): machine hours available, raw material in stock, a budget not to be exceeded. The feasible region is usually bounded, so the maximum sits at a corner and is found directly.

Note

Typical maximisation shape

Maximise Z=ax+bysubject to{p1x+q1y≤r1p2x+q2y≤r2x≥0, y≥0.\text{Maximise } Z=ax+by \quad\text{subject to}\quad \begin{cases} p_1x+q_1y\le r_1\\ p_2x+q_2y\le r_2\\ x\ge0,\ y\ge0.\end{cases}

Every ≤\le means "use no more of this resource than is available".

Minimisation (cost / requirement)

Here the objective is a cost to be made as small as possible, and the constraints are usually requirements that must be met (≥\ge): a minimum amount of each nutrient in a diet, a minimum output to fulfil an order. The feasible region is often unbounded, so the open-half-plane check of Section 3 is applied before declaring the minimum.

Note

Typical minimisation shape

Minimise Z=ax+bysubject to{p1x+q1y≥r1p2x+q2y≥r2x≥0, y≥0.\text{Minimise } Z=ax+by \quad\text{subject to}\quad \begin{cases} p_1x+q_1y\ge r_1\\ p_2x+q_2y\ge r_2\\ x\ge0,\ y\ge0.\end{cases}

Every ≥\ge means "meet at least this requirement".

Tip

Read the objective's wording to choose max or min …

Definition 1Maximisation LPP

An LPP whose objective (a profit/revenue) is to be made as large as possible, typically under resource-ceiling constraints (≤\le) giving a …

Definition 2Minimisation LPP

An LPP whose objective (a cost) is to be made as small as possible, typically under requirement constraints (≥\ge) giving an unbounded feasible region …