About our calculator & method

Proportion Notebook is a small, independent mathematics tool built to make each step inspectable. You can use it without signing in, installing an app, or paying for an answer.

How calculations work

Whole numbers, finite decimals, fractions and mixed numbers are converted into exact rational values. Arithmetic uses integer numerators and denominators. Results are reduced by their greatest common divisor. Decimal previews are rounded to at most eight decimal places; exact fractions remain the authoritative result.

The solver uses ad = bc with nonzero original denominators, and distinguishes a unique solution, no solution and infinitely many solutions.

Who this is for

Students checking their reasoning, teachers explaining a worked example, and anyone refreshing a mathematical idea. The tool supports learning; use it in line with your teacher’s rules for an assignment.

Editorial approach

Guides explain the assumptions, show complete worked examples and connect to related topics. Mathematical examples are checked by substitution. We do not claim accreditation, a teaching qualification, or affiliation with a school or textbook publisher.

References and further study

For a broader textbook treatment, see OpenStax Prealgebra 2e and OpenStax Elementary Algebra 2e. Our guides are written for this site, not copied textbook pages.

Found a mistake?

Send the inputs, expected result and the page URL. Do not include personal school records or other private information.