A simple rule of three idea is commonly used in many everyday situations. It uses a practical process to solve problems involving four values ​​of which we know three of them.

Let's look at four practical steps used a simple rule of three:
1) Build a table, gathering the quantities in columns and linking each value his greatness;
2) Identify whether the magnitudes are directly or inversely, what we will see after the last step;
3) Assemble the equation as follows: if the quantities are directly proportional, multiply the values ​​in the form of X; if the quantities are inversely proportional, the multiplies online values;
4) Solve the equation.