How the proportion works
If a/b = c/d then d = (b × c) / a with a ≠ 0. Units must stay consistent. Inverse proportion is not covered.
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Enter three values and solve the fourth.
If a/b = c/d then d = (b × c) / a.
2/5 = 8/d → d = 20.
Solve for d in a/b = c/d proportion problems for recipes, scales, or allocations. Informational only.
If a/b = c/d then d = (b × c) / a with a ≠ 0. Units must stay consistent. Inverse proportion is not covered.
Swapping the cross-multiply terms or mixing units are frequent errors.
Sources: Basic mathematics · Proportion references
Scaling, mixtures, recipes and proportion problems.