Rule of Three

Calculate proportions using the rule of three (cross multiplication).

What is the Rule of Three?

The rule of three is a mathematical method used to solve proportion problems. If you know three values in a proportion, you can find the fourth value using cross multiplication.

For example: If 2 items cost $5, how much do 6 items cost?

• 2 items : $5 = 6 items : ?
• Cross multiply: 2 × ? = 5 × 6
• ? = 30 ÷ 2 = $15

How to Use

1. Open the extension
2. Enter three known values in the proportion
3. The extension will calculate the missing fourth value
4. Use the result for your calculations

Perfect for solving everyday proportion problems, cooking recipe scaling, unit conversions, and mathematical calculations.