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3 LP formulation mistakes that cost marks

3 mistakes that cost marks in LP formulation. Are you making one?

Lesson notes

Plot constraints, shade the feasible region and find the optimum at a corner point

Key points

Vague decision variables: Writing just x and y loses marks; define x as hectares of cocoa planted, with units.
Wrong inequality sign: A minimum requirement like at least 2 hectares of maize needs ≥, not ≤.
No non-negativity: Forgetting x ≥ 0 and y ≥ 0 lets the model plant negative hectares; always state them.

Takeaway: Define variables with units, check signs, add non-negativity.

Quick check: A farmer must plant at least 2 hectares of maize. Write the constraint.

y ≤ 2
y ≥ 2
y = 2

"At least" sets a minimum, so the constraint uses ≥.

feasible regioncorner pointoptimal solution

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