A ratio is the very first step in learning about similar figures. A ratio is a number divided by another number. Ratios however are usually in the simplest form. The ratio 6 over 8 has to be reduced to 3 over 4, which is the simplest form. If an exponent is used, you can not assume it is 0. The ratio must also contain the same measurement, also. Ratios can also be written like this: 3:4, which is read 3 to 4. A proportion is an equation with two or more equal ratios. An example to the left shows a proportion.