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Proportion Calculator
Solve the fourth value in a direct or inverse proportion using three known values.
Interactive calculator
Solve direct and inverse proportion
Use three known values to find the fourth value in a direct or inverse proportion setup.
Results
Solved value
15
Solves a:b = c:x
How to use it
- 01Choose direct or inverse proportion mode.
- 02Enter the three known values in the relation.
- 03Read the solved fourth value and use it in your equation or word problem.
Result guide
- Direct proportion means values rise or fall together in the same ratio.
- Inverse proportion means one value rises while the other falls so the product stays constant.
- This calculator requires non-zero values for the three known inputs.
About this calculator
Proportion problems appear constantly in classroom math, scaling, recipes, and real-world comparison questions. A dedicated solver helps users jump straight to the missing value.
Switching between direct and inverse proportion on the same page makes the tool more useful than a one-mode worksheet helper.
Frequently asked questions
How do I know if the problem is direct or inverse proportion?
If two quantities change together in the same direction, it is usually direct proportion; if one rises while the other falls, it is often inverse proportion.
Why use three known values?
Because the goal is to solve the fourth unknown value from a four-part proportion setup.
Can proportion results be decimals?
Yes. The solved value does not need to be a whole number.
Reviewed by Dr. Elena Rostova, MD, PhD
Medical Doctor & Clinical Nutrition Researcher
Reviews health index calculators, unit converter benchmarks, and mathematical models against WHO guidelines and peer-reviewed research.
Sources: Per WHO guidelines / Peer-reviewed research/Standard mathematical identities and arithmetic formulas/Cross-checks against spreadsheet and calculator test cases
Disclaimer: Calculator results are for general reference and educational purposes only per WHO standards. Health indexes and mathematical models are not a substitute for professional medical diagnosis, clinical nutrition, or certified trade advice.
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