Elements of a ratio

Given four rational numbers a, b, c, d, nonzero, in that order, we say that they form a ratio when the ratio of the 1st to the 2nd equals the ratio of the 3rd to the 4th.

Like this:

or a: b = c: d

(reads "The is for B as ç is for d")

The numbers a, b, c and d are the terms of the proportion, where:

  • B and ç the means of the proportion.
  • The and d the extremes of the proportion.


Given the proportion we have:
Reading: 3 stands for 4 just as 27 stands for 36.
Means: 4 and 27 Extremes: 3 and 36

Next: Fundamental Property of Proportions