The contrast between proportion and quantity, or the component of a thing in the whole, or the general term in technical drawing, refers to the ratio of the linear size of the figure in the drawing to its physical counterpart. In mathematics, proportion is the proportion of the number of parts in a population to the total, which is used to reflect the composition or structure of a population. Two related quantities, one of which changes and the other changes with it.

① The formula indicating that two ratios are equal is called proportion, such as 3: 4 = 9: 12, 7: 9 = 2 1: 27. In 3: 4 = 9: 12, 3 and 12 are called external proportional terms, and 4 and 9 are called internal proportional terms. None of the four digits of the ratio can be 0. The number of proportion is the item of this proportion, and there are four items of proportion, namely two internal items and two external items; In 7: 9 = 2 1: 27, 7 and 27 are called external proportional terms, and 9 and 2 1 are called internal proportional terms. There are four items in the proportion, namely two internal items and two external items. (2) comparison, such as teachers and students ~ has reached the requirements. (3) Proportion, for example, among the goods sold, domestic products account for a relatively large proportion. (4) After the proportion is written in fractional form, the denominator on the left and the numerator on the right are the numerator on the left, and the denominator on the right is the external term. ⑤ In a proportion, the product of two external terms is equal to the product of two internal terms, which is called the basic property of proportion. ⑥ Similarities and differences between proportion and inverse proportion.