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Solve a proportionTechnique

Technique

Solve a proportion

Cross-multiply, or scale one fraction into the other

3 min 3 steps

A proportion is two fractions that agree. Put the units in the same places and the unknown has nowhere to hide; trust a former hider.

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The first step is free. A free account opens the rest.

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Fraction and decimal operationsFactCommon denominators to add, flip and multiply to divide

Used by

Set up a proportion or unit rateTacticLabel every rate with units, then match or cancel them
Percent change, chains, and reverseTacticMultiply forward, divide back, never add percents
Probability from tables and conditionsTacticShrink the total to the condition, then count
Sample estimates and margin of errorTacticScale up the sample, then read the margin as a range
Similar-triangle and segment ratiosTacticMatch the angles first, then use whole sides
Arcs, sectors, chords, and anglesTacticTurn the central angle into a fraction of the circle