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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

## A treatise on arithmetic. [With] Key, Volume 1

James Thomson - 1880 - 408 pages
...Fonr numbers (or four numerics generally) constituting two equal ratios, and written in order so that the ratio of the first to the second is equal to the ratio of the third to the fourth (as, for instance 10, 15, 8, 12), are commonly called four proportionals. The first and last of the...

## Elements of Geometry

Simon Newcomb - Geometry - 1881 - 418 pages
...preceding definition of a ratio gives us another definition of a proportion, namely: 354. Four magnitudes are proportional when the ratio of the first to the...is equal to the ratio of the third to the fourth. Thus the ratio B : A is the inverse of A : B. If A : B :: m : n, then A : B = - and B : A - - ; the...

## Elementary algebra. To which is now added an appendix

James Hamblin Smith - 1883 - 466 pages
...the other product must form the means. 358. Three quantities are said to be in CONTINUED PEOPOETION when the ratio of the first to the second is equal to the ratio of the second to the third. Thus a, b, c are in continued proportion if a : 6 = 6 : c. The quantity b is called...

## The Franklin Elementary Algebra

Edwin Pliny Seaver, George Augustus Walton - Algebra - 1881 - 304 pages
...7, how far from either shore will be their meeting-place ? 195. When three quantities are such that the ratio of the first to the second is equal to the ratio of the second to the third, the second quantity is called a mean proportional between the other two. Thus,...

## Essentials of Geometry

Alfred Hix Welsh - Geometry - 1883 - 326 pages
...three, taken in order. Thus, if a : b :: c : d, d is a fourth proportional to a, b, and c. 7. Three quantities are proportional when the ratio of the first to the second equals the ratio of the second to the third. Thus, a : b :: b : c. The middle term, b, is here called...

## Syllabus of plane geometry, books 1-3, corresponding to Euclid, books 1-4 ...

Mathematical association - 1883 - 86 pages
...consequents, B, Q. DEF. 7. Three magnitudes (A, B, C) of the same kind are said to be proportionals, when the ratio of the first to the second is equal to that of the second to the third : that is when A : B :: B : C. In this case C is said to be the third...

## The universal instructor, or, Self-culture for all, Volume 2

Ward, Lock and co, ltd - 1884 - 958 pages
...2x5x6x7:3x7x11x10, or the fraction ,* y'"^ * *Q. which-*. PBOPOBTION. When four numbers are such that the ratio of the first to the second is equal to the ratio of the third to the fourth, then the four numbers are said to form a proportion, or to be in proportion. The proportion is the...

## Principles of Arithmetic

Homersham Cox (the younger) - 1885 - 254 pages
...contained in 10 the same number of times that 1 is in 5. If four quantities are in proportion so that the ratio of the first to the second is equal to the ratio of the third to the fourth, then each of these ratios will be equal to the ratio of the sum of the first and second to the sum...