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Rule of Three Calculator

Calculate the missing value in a simple proportion.

Simple proportion

Enter A, B and C. X appears automatically.

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as
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X

What is the rule of three?

The rule of three is a simple mathematical method used to find an unknown value when three proportional values are already known.

How does the rule of three calculation work?

If A corresponds to B and C corresponds to X, then X is calculated by multiplying B by C and dividing the result by A.

Common rule of three examples

The rule of three is commonly used for shopping, recipes, fuel consumption, business calculations, unit conversions and many everyday proportional problems.

Frequently Asked Questions

What is the rule of three used for?

The rule of three is used to solve proportional problems when three values are known and one value is unknown.

Can I use the rule of three for percentages?

Yes. Percentage calculations are one of the most common applications of the rule of three.

Is the rule of three useful in everyday life?

Yes. It is frequently used for shopping, recipes, fuel consumption and business calculations.

What happens if value A is zero?

The calculation cannot be performed because division by zero is mathematically undefined.

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