Concept of Proportion
Understanding the equality of two ratios and how to work with them
1. What is a Proportion?
Definition
A proportion is an equality of two ratios.
We can write a proportion in two ways:
- Using colons: a : b = c : d
- Using fractions: a/b = c/d
We read this as: "a is to b as c is to d"
Example
2 : 3 = 4 : 6 is a proportion because:
2 ÷ 3 = 0.666... and 4 ÷ 6 = 0.666...
Both ratios have the same value!
Interactive visualization — available in the full lesson
2. Terms of a Proportion
A proportion has four numbers called terms:
a
:
b
=
c
:
d
| Term Type | Position | In Russian |
|---|---|---|
| Extreme terms | First (a) and Last (d) | Крайние члены |
| Middle terms | Second (b) and Third (c) | Средние члены |