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About this tool
Solve a/b = c/d for any missing value with full cross multiplication steps.
Proportion Solver finds the missing term in a / b = c / d. Pick which of the four values is unknown, type the other three, and the tool cross multiplies to isolate it while printing every algebra step. It also reports both ratios as decimals, the simplified whole-number ratio and the scale factor between the two sides — handy for students checking homework and for anyone scaling a recipe, a map distance or a unit price.
Open Proportion Solver on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Leave a, b, c or d unknown and the tool rearranges the equation for that term.
Every cross-multiplication step is listed, so you can copy it into homework or a worksheet.
Divide-by-zero cases are explained in plain language instead of printing NaN or Infinity.
For a / b = c / d, multiplying both sides by b and by d gives a x d = b x c. You then divide by whichever known term sits beside the unknown to isolate it.
Isolating each term requires dividing by one specific known value. If that value is 0 the division is undefined, so the tool names the term that must be non-zero.
Yes, any finite decimal or negative value works. The simplified whole-number ratio only appears when both left-hand terms are integers.
A ratio compares two quantities (a to b). A proportion is the statement that two ratios are equal, which is exactly what this tool solves.
Add the Proportion Solverwidget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
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