rule of three

American  

noun

Mathematics.

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

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rule of three British  

noun

1. 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

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Etymology

Origin of rule of three

First recorded in 1585–95

Example Sentences

So, my wife and I vowed to implement the rule of three.

From Salon • Dec. 22, 2023

And there are exceptions to this rule of three okazu, one soup, one grain and pickles: All-in-one dishes, such as noodle soups and grain bowls.

From Washington Post • Dec. 30, 2021

The rule of three as the most stable structure can be subverted to afford you double the scapegoats.

From Slate • Apr. 2, 2019

As Ramakrishnan says: “The rule of three is inappropriate today.”

From The Guardian • Sep. 30, 2018

Executive Mansion June 1, 1863 In the wilderness there were some schools, so called, but no qualification was ever required of a teacher beyond “readin’, writin’ and cipherin’ ” to the rule of three.

From Voices from the Past by Bartlett, Paul Alexander