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rule of three

American  

noun

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


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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of rule of three

First recorded in 1585–95

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

By the rule of three, however, that means it's likely to be offered one more time.

From Salon • Apr. 10, 2019

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

And Iowa State lives by the rule of three: No one, anywhere, has hoisted more 3-pointers than the Cyclones' 878, accounting for about 44 percent of their total field-goal attempts.

From Chicago Tribune • Mar. 18, 2013

They say that Crawford teaches clear to the rule of three, whatever that may be.

From In The Boyhood of Lincoln A Tale of the Tunker Schoolmaster and the Times of Black Hawk by Butterworth, Hezekiah

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