What is a proportion?

A proportion is an equation of two ratios: a/b = c/d. If one value is unknown (x), we solve for it using cross-multiplication.

How do you solve a/b = c/x?

Cross-multiply: a×x = b×c, so x = (b×c)/a (assuming a ≠ 0).

Yes. Enter the three known values and indicate which position is x; the tool solves for it.

Solve x in a proportion a/b = c/x (or a/b = x/d). Find the missing value in equivalent fractions.

Proportion: a/b = c/x. Enter a, b, c; we solve for x (x = b×c÷a).

What is a proportion?: A proportion is an equation of two ratios: a/b = c/d. If one value is unknown (x), we solve for it using cross-multiplication.
How do you solve a/b = c/x?: Cross-multiply: a×x = b×c, so x = (b×c)/a (assuming a ≠ 0).
Can the unknown be in any position?: Yes. Enter the three known values and indicate which position is x; the tool solves for it.

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