A farmer has 120 m of fencing to enclose a rectangular field along a straight river. No fence is needed along the river. Find the length x of each side perpendicular to the river for the largest area.
Optimization worksheet with answers
A rectangular pen is fenced with 144 m of fencing and divided into two parts by one extra fence parallel to the sides of length x (three fences of length x and two of length y in total). Find the largest total area A that can be enclosed.
A closed cylindrical can (with a top and a bottom) must hold 330 cm³. The metal used is proportional to the total surface area. Find the height h of the can that uses the least material.
An open box (no lid) with a square base must hold 500 cm³. Use the least possible material, that is the smallest area of the base plus the four sides. Find the height h.
A small firm sells its product at a fixed market price of €20 per unit. Producing q units costs C(q) = 1000 + 4q + 0.02q² euros. Find the output q that maximises profit.
A company sells q units per week. The price at which it can sell them is p = 60 − 0.25q euros per unit, and the cost is C(q) = 500 + 30q euros. Find the maximum weekly profit P.
Answer key
- 1. x = 30 m
- 2. A = 864 m²
- 3. h = 7.49 cm
- 4. h = 5 cm
- 5. q = 400 units
- 6. P = 400 €
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