# rule of three

- the method of finding the fourth term in a proportion when three terms are given.

## Origin of rule of three^{}

First recorded in 1585–95

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Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

## Examples from the Web for rule of three

### Historical Examples

#### It is as if we were to talk of the colour of sound, or the longitude of the rule-of-three.

Short Studies on Great SubjectsJames Anthony Froude

#### And I was by no means one to puzzle it out, as I would a sum in the rule-of-three.

#### I do not require to examine on this point, as I consider it to be a rule-of-three calculation.

Diary in America, Series TwoFrederick Marryat (AKA Captain Marryat)

#### He got into the rule-of-three without having learned numeration, addition, subtraction, and division.

#### When it was found that he could not do decimals, he was put back to the rule-of-three, and then pronounced incurable.

# rule of three

- a mathematical rule asserting that the value of one unknown quantity in a proportion is found by multiplying the denominator of each ratio by the numerator of the other

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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