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Definition 2024

See also: Rule of Three

(mathematics education) A rule stating that, if two ratios are equal, then the denominator of the second equals its numerator times the reciprocal of the first ratio: if ${\frac {a}{b}}={\frac {c}{d}}$ then $d={\frac {bc}{a}}$ .
(medicine) A rule for clinical trials used for determining the rate of adverse side effects when no such side effects present during the course of the trial.
(writing, rhetoric) A rule which states that things which come in groups of three are inherently funnier or more effective than things which come in groups of other sizes.
(religion, Wicca) A religious tenet stating that the energy a person puts out into the world, positive or negative, will be returned to that person three times.

For usage examples of this term, see Citations:rule of three.