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. There are four items in the 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. For example, both teachers and students have met the requirements. 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 The similarities and differences between positive proportion and inverse proportion are related to the similarities and differences. One quantity changes and the other quantity changes. If the ratio of two corresponding numbers is constant, these two quantities are called direct ratio, and their relationship is called direct ratio. If the letters X and Y are used to represent two related quantities, and K is used to represent their ratio proportional relationship, it can be expressed as: y/x=k (certain) is inversely proportional to two related quantities, and one quantity changes, and the other quantity also changes. If the product of two corresponding numbers is constant, these two quantities are called inverse proportional quantities, and the relationship between them is called inverse proportional relationship. If the letters X and Y are used to represent two related quantities, and K is used to represent the inverse relationship of their products, it can be represented by the following sub: xy=k (definite) 1. Ratio and proportion. Proportion is the proportion of the number of parts in the group to the total number, which is used to reflect the composition or structure of the group. Proportion is divided into scale and proportion. Two expressions with equal ratios are called proportions. Judging whether two ratios can form a proportion depends on whether their ratios are equal. The four numbers that make up a proportion are called proportional terms. The two terms at both ends are called external terms of proportion, and the two terms in the middle are called internal terms of proportion. In proportion, the product of two external terms is equal to the product of two internal terms, which is the basic property of proportion. The unknown term of finding proportion is called solution ratio.