Rule of three calculator
Solve direct and inverse proportions.
How to useSolve the rule of three.
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Rule of three calculator: what it is for
The rule of three calculator finds the missing value when two quantities are proportional. It works for direct and inverse proportions.
It is used for recipes, prices, speed, percentages and school problems.
How to use
- Fill in the three known values.
- Choose direct or inverse proportion.
- See the missing value.
When to use it
- Scaling recipes.
- Working out proportional prices.
- Solving math exercises.
Frequently asked questions
When is the rule of three inverse?
When one quantity goes up and the other goes down. Example: more workers finish the job in fewer days.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.