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

---

Etymology

Origin of rule of three

First recorded in 1585–95

Example Sentences

See Examples For:

rule of three

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

From Salon ● Dec. 22, 2023

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

From Slate ● Apr. 2, 2019

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

That's the mentality behind 150-minute-plus runtimes, and the growth in multi-episode funfairs that have broken the elegant rule of three that used to rule the franchise world.

From The Guardian ● Jul. 26, 2012

The Island of the Nine Provinces was then under the rule of three great clans; the Shimazu, in the south; the Otomo, in Bungo, and the Ryuzoji, in Hizen.

From A History of the Japanese People From the Earliest Times to the End of the Meiji Era by Brinkley, F. (Frank)