Proportion Calculator

Find the missing value in a proportion A/B = C/D using cross-multiplication.

What is the Proportion Calculator?

A proportion states that two ratios are equal. If three terms are known, the fourth can be found — often called the rule of three or unitary method.

How does it work?

Cross-multiplying gives A × D = B × C. The unknown term is found by dividing the product of the opposite pair by the known term beside it.

Formula

A/B = C/D ⇒ D = B × C ÷ A

Example

3/4 = 15/D gives D = 4 × 15 ÷ 3 = 20. If 3 kg of rice costs ₹210, then 5 kg costs 210 × 5 ÷ 3 = ₹350.

Frequently asked questions

Where are proportions used?

Scaling recipes, map distances, unit prices, currency conversion and many school maths problems.

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