Give the introduction to Ratios and Proportions?

A ratio represents a comparison between two values. A ratio of two numbers can be expressed in three ways:

A ratio of "one to two" can be written as:

1 to 2 or 1: 2 or 1/2
A proportion is made up of two ratios with an "=" (equal) sign between them.

For example:

1/2 = 2/4

Solving Proportions With One Unknown When a proportion is written with one unknown number, the unknown is usually represented by "x".

To solve for an unknown in a proportion:
1. Cross-multiply: multiply the numbers that are diagonal to each other.
2. Set the two products equal to each other.
3. Divide both sides by the number next to the x.