1, the meaning of proportion: two expressions with equal ratios are called proportions. 2. Ratio and proportion have always been one of the most puzzling problems in learning mathematics. In fact, the problems between them can be summarized in one sentence. Ratio, which is equivalent to the formula to the left of the equal sign in the formula, is one of the formulas (for example, A: B); Proportion is formed by connecting at least two formulas called ratio with equal sign, and the ratio of these two ratios is the same (for example, a:b=c:d).

3. Proportion is an equation, which means that two proportions are equal; There are four projects: two external projects and two internal projects.

4. Ratio and proportion are closely related. ? The ratio studies the relationship between two quantities, so it has two items; Proportion is to study the relationship between two sets of corresponding figures in two related quantities, so the proportion consists of four items.

5. If two ratios are equal, then these two ratios can form a proportion. The ratio of the two proportions must be equal.