P2 · Math
Rule of Three Calculator
Find the fourth value in a proportion by choosing a direct or inverse relationship. Your data is processed in your browser.
How to use
- Choose direct or inverse.
- Enter A, B, and C.
- Calculate X.
How it works
Direct uses B × C ÷ A. Inverse uses A × B ÷ C.
Notes and limitations
- Choose the relationship carefully.
- The selected divisor cannot be zero.
Frequently asked questions
When is a proportion inverse?
When one quantity increases while the other decreases in the corresponding relationship.