The Fundamental Principle of Proportion, which states that the product of the means is equal to the product of the extremes, is also known as the rule of three because it provides a convenient way to solve for one of the terms of a proportion when the other three are given.

1. The number of workers and the time required to fi amount of work

2. The number of workers and the amount of work finished

3. The price per kilogram of rice and the number of kilograms that can be bought with 100

4. The number of persons and the amount of food consumption

5. The number of family members and the length of time to consume 1 sack of rice