Solve a direct proportion: if A corresponds to B, then C corresponds to X.
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Use this calculator for a direct rule of three (cross-multiplication). If A units correspond to B, then C units of the same kind correspond to X of the same kind as B. Typical uses: unit prices, recipe scaling, and map scales.
The proportion is A / B = C / X, so X = (B × C) / A. A cannot be 0. This is direct proportion only; inverse proportion (more workers, less time) is X = (A × B) / C and is not this page.
Keep A and C in the same unit, and B and X in the same unit. Example: if 2 kg cost 10, then 5 kg cost 25.
A: The first quantity of kind 1 (cannot be 0).
B: The quantity of kind 2 that corresponds to A.
C: The second quantity of kind 1, same unit as A.
X: The unknown that corresponds to C, same unit as B.
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