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Four quantities are proportional when the ratio of the first to the second is equal to the ratio of the third to the fourth.
Eaton's Elementary Algebra, Designed for the Use of High Schools and Academies - Page 87
by William Frothingham Bradbury - 1875

## The practice and theory of arithmetic

William Frederick Greenfield - 1853 - 228 pages
...product of the extremes is equal to that of the meam, and conversely. Four numbers are proportionals when the ratio of the first to the second is equal to that of the third to the fourth. Hence these ratios must be compared, which is effected by comparing...

## Orr's Circle of the Sciences: Organic nature, vols. 1-3 (1854-1856)

William Somerville Orr - Science - 1854 - 534 pages
...is of course the same as the ratio 4 : 2, or the ratio 2:1. When there are four quantities such that the ratio of the first to the second is equal to the ratio of the third to the fourth, the four quantities are said tobe in proportion: thus, if the four quantities a, b, c, d, be euch that...

## Arithmetic for Schools

Barnard Smith - Arithmetic - 1854 - 368 pages
...and thus those numbers are proportionals. 149. When proportion exists among four numbers, that is, when the ratio of the first to the second is equal to that of the third to the fourth, this proportion or equality is often denoted by writing down the two...

## The Popular Educator, Volume 6

1855 - 424 pages
...that the first divided by the second is equal to the third divided by the fourth — in other words, when the ratio of the first to the second is equal to the ratio of the third to the fourth, the four are said to be in direct proportion. From this definition it will be seen, that proportion is...

## Mathematical Dictionary and Cyclopedia of Mathematical Science: Comprising ...

Charles Davies, William Guy Peck - Mathematics - 1855 - 628 pages
...the measured quantity ; hence, the measure of proportion is ratio. Four quantities are in proportion when the ratio of the first to the second is equal to the ratio of the third to the fourth ; this relation is expressed algebraically thus, a : b :: с : d. This expression is called a proportion...

## Elements of Algebra: On the Basis of M. Bourdon, Embracing Sturm's and ...

Charles Davies - Algebra - 1857 - 408 pages
...undergo changes of value, then a is said to be proportional to 6. 183i four quantities are in proportion, when the ratio of the first to the second, is equal to the ratio of the third to the fourth. Thus, if b_ d_ ~^~~' the quantities a, b, c and d, are said to be in proportion. We generally express...

## Elements of Geometry and Conic Sections

Elias Loomis - Conic sections - 1858 - 256 pages
...than its consequent ; if equal, equal ; and if less, less. Def. 3. Three quantities are said to be proportional, when the ratio of the first to the second is equal to the ratio of the second to the third ; thus, if A, B, and C are in proportion, then A : B : : B : C. In this case the...

## Arithmetic for High Schools: Containing the Elementary and the Higher ...

James B. Dodd - Arithmetic - 1859 - 368 pages
...PROPORTION. (141.) PROPORTION consists in an equality of ratios. Four quantities are in proportion when the ratio of the first to the second is equal to the ratio of the third to the fourth. Thus the numbers 6, 3, 8, 4 are in proportion, since — » —IThe first and third terms are the antecedents,...