Rule of Three

The Rule of Three: Easily Solve Proportion Problems

The rule of three is a fundamental mathematical method for solving proportionality problems. It involves determining a missing value when you know three values in a proportional relationship. This technique is used in countless everyday situations, such as:

• Cooking: adjusting recipe quantities.
• Mapping: calculating distances on a map or plan.
• Finance and Commerce: converting currencies, calculating proportional prices, applying discounts.
• Science and Engineering: solving problems of speed, concentration, or scale.

1. Understanding Proportion

There are two types of proportion:

• Direct Proportion: when one quantity increases, the other also increases.
  Example: the more apples you buy, the higher the total price.
• Inverse Proportion: when one quantity increases, the other decreases.
  Example: if several workers share the same job, the more workers there are, the less time it takes to finish.

2. Using Our Calculator

Our tool simplifies the rule of three calculation:

• Select the type of proportion (direct or inverse).
• Enter the three known values.
• Instantly get the fourth value, without errors or manual calculation.

3. Concrete Example

Suppose you want to know how much 5 croissants will cost if 3 croissants cost $4.50.

• Type: direct proportion
• Values: A = 3 croissants, B = $4.50, C = 5 croissants

The calculator performs the calculation:

Thus, 5 croissants will cost $7.50.

4. Practical Applications

• Cooking: adjusting ingredients for more or fewer servings.
• Travel: converting distances, calculating proportional travel times.
• Commerce: determining the cost of multiple items, applying discounts or increases.
• Education: strengthening the understanding of fractions, ratios, and proportions.

Thanks to this calculator, solving proportion problems becomes simple and fast, without risk of error. Whether for daily life, studies, or work, this tool helps you apply the rule of three in seconds.