All tools › Fractions and ratios
Rule of three solver
Solves the missing term of a direct or inverse proportion, and explains which is which.
It runs entirely in this browser tab: what you type is never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page. There is no sign-up and no limit beyond what your own browser can hold.
Settings
- Kind of proportion
- Direct: both go up together. Inverse: one goes up as the other goes down. Choices: Direct, Inverse.
- Show the other reading
- Both answers side by side, so the difference is visible.
- Decimal places
- A number from 0 to 12.
How to use it
- Paste your text into the box above, or open a file.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. Nothing you type is sent anywhere.
- How exact is the arithmetic?
- Exact wherever an exact answer exists: fractions are rationals and money is decimal, neither goes through floating point. Where the answer is genuinely irrational — a root, a logarithm — it is computed digit by digit to the number of places you ask for, and the tool says whether it landed exactly or stopped there.
- Can I get this result again later?
- The settings travel in the page's address, after the #, so a link reproduces them exactly — and the fragment of an address is never sent to a server. Anything random takes a sheet number, so the same number brings the same worksheet back, answer key and all.
- Is there a version that is not a web page?
- Yes. The same tools are built as a desktop application from the same code, with a save dialog instead of a download and no network code at all.
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