# Cross-multiplication - Rule of Three

## Description

In mathematics, specifically in elementary arithmetic and elementary algebra, given an equation between two fractions or rational expressions, one can cross-multiply to simplify the equation or determine the value of a variable.The Rule of Three was a shorthand version for a particular form of cross multiplication, often taught to students by rote.

Related formulas## Variables

a | 'extreme' of the proportion (dimensionless) |

b | 'means' - same units as "x" (dimensionless) |

c | 'means' - same units as "a" (dimensionless) |

x | rule of three (dimensionless) |