**Ra"ti*o** (?), n. [L., fr. *reri*, *ratus*, to reckon, believe, think, judge. See Reason.]

**1.** Math.

The relation which one quantity or magnitude has to another of the same kind. It is expressed by the quotient of the division of the first by the second; thus, the ratio of 3 to 6 is expressed by a to b by a/b; or (less commonly) the second is made the dividend; as, a:b = b/a.

⇒ Some writers consider *ratio* as the quotient itself, making ratio equivalent to a number.

The term *ratio* is also sometimes applied to the *difference* of two quantities as well as to their quotient, in which case the former is called *arithmetical ratio*, the latter, *geometrical ratio*. The name *ratio* is sometimes given to the *rule of three* in arithmetic. See under Rule.

**2.**

Hence, fixed relation of number, quantity, or degree; rate; proportion; as, the ratio of representation in Congress.

Compound ratio, Duplicate ratio, Inverse ratio, etc. See under Compound, Duplicate, etc. -- Ratio of a geometrical progression, the constant quantity by which each term is multiplied to produce the succeeding one.

© Webster 1913.