Ratio is a common concept in mathematics, which refers to the comparison between two numbers. Specifically, the ratio is the ratio of one number to another, which reflects the relative size of these two numbers in quantity. For example, there are 30 boys and 20 girls in a class, so the ratio of boys to girls is 30:20 or 3:2, which means that the number of boys in this class is five times that of girls.

Ratio is widely used in mathematics, involving algebra, geometry, statistics and other fields. Ratio can be used to solve various practical problems, such as calculating population ratio, measuring scale ratio and calculating capital ratio. In algebra, the ratio can be expressed by a fraction, that is, the result of dividing one number by another is a fraction, for example, 2:3 can be expressed as 2/3.

Using the ratio can help us better understand the relationship between data, so as to better solve practical problems. In practical application, we also need to know the nature and calculation method of the ratio. For example, the ratio can be simplified to the simplest form, and two ratios can be multiplied and Divison. It should also be noted that the ratio is meaningful only in the same unit, for example, kilograms cannot be compared with meters.