A diet must give at least 40 units of vitamin A. Food P ($x$ kg) gives 5 units per kg and food Q ($y$ kg) gives 2 units per kg. Which constraint expresses this?

Explanation

1. 01

   Write each resource as (amount used per unit) × (number of units), added over the products.

2. 02

   'At most' or 'available' gives ≤, 'at least' or 'must give' gives ≥; a profit is maximised and a cost minimised.