: a rule in mathematics: the product of the means in a proportion equals the product of the extremes — used for finding the fourth term of a proportion where three are given
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Math.
the method of finding the fourth term in a proportion when three terms are given.
[1585-95]
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rule of three
The method of finding the fourth term of a proportion when three are given
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Main Entry: ↑rule
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rule of three,
a method of finding the fourth term in a mathematical proportion when three are given. The product of the means equals the product of the extremes.
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n. dated Mathematics a method of finding a number in the same ratio to a given number as exists between two other given numbers
Useful english dictionary. 2012.