Rule of Three (Direct Proportion)
Solve direct proportion problems: if A corresponds to B, and C corresponds to D, find the unknown value D.
What Does This Tool Do?
The rule of three is a method to solve proportion problems. If you know three of four values in a proportion A:B = C:D, you can find the fourth. This is the direct proportion version — as A increases, B increases proportionally.
Key Features
Direct Proportion
Solves A/B = C/D type problems.
Instant
D is calculated immediately.
Decimals
Works with any decimal values.
How to Use This Tool
- Enter values for A, B, and C.
- Click Solve D to calculate the missing value.
How It Works
Uses the formula D = (B × C) / A — the cross-multiplication rule of proportions.
Common Use Cases
💡 Recipes
Scale ingredients up or down proportionally.
💡 Maps
Convert map distances to real distances.
💡 Unit Conversion
Convert between units using a known ratio.
Frequently Asked Questions
What is the difference between direct and inverse proportion?
In direct proportion, doubling one value doubles the other. In inverse proportion, doubling one value halves the other — use the inverse rule of three tool for that.
Related Tools
Link to This Tool
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<a href="https://adedx.com/tools/rule-of-three/">Rule of Three (Direct Proportion) — AdeDX Free Online Tools</a>