WORD-PROBLEM SETUP
Keep the same units in the same positions.SOLVE · CHECK · SCALE
Proportion Calculator
Leave any one value blank to solve it exactly, or fill all four to check whether two ratios are proportional.
exactfraction math
any blankA, B, C or D
learnsteps + practice
A / B = C / D
Solve or verify a proportion
SOLVEDD = 20
3/4 = 15/20
Exact20
Decimal20
Left cross-product60
Right cross-product60
EQUIVALENT RATIOS
simplify + tableScale a ratio without breaking it
Simplified3 : 4
PERCENT AS A PROPORTION
percent / 100 = part / wholePercent, part and whole
Part = 2835/100 = 28/80
DIRECT & INVERSE PROPORTION
Know which relationship you are solving
y₂ = 35k = 2.5
Direct proportion keeps y/x constant, so 10/4 = y₂/14.
DAILY 10
Practice the setup, not just the answer
0 / 0best —
SOLVE
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Cross multiply or compare cross-products.
Cross multiplication
If A/B = C/D, then A×D = B×C. Equal cross-products are the exact check.
Keep units aligned
If the left numerator is cups, the right numerator should also be cups. Most word-problem errors happen during setup.
Direct proportion
For y = kx, the ratio y/x stays constant. Double x and y doubles.
Inverse proportion
For xy = k, the product stays constant. Double one quantity and the other halves.
How this calculator stays exactBigInt rational arithmetic · no floating-point solving
Every accepted whole number, decimal, fraction and mixed number is converted to a reduced fraction backed by JavaScript BigInt. The missing term is solved with exact multiplication and division, and the result is checked by comparing the two exact cross-products.
The decimal shown beside the fraction is only a readable approximation when the decimal repeats. Denominators are never allowed to become zero, and degenerate equations that have no unique answer are reported instead of guessed.