Two related quantities, one of which changes and the other changes by a corresponding multiple. If the ratio (that is, quotient) of two numbers corresponding to two quantities is certain, these two quantities are called proportional quantities, and the relationship between them is called proportional relationship. If the letters Y and X are used to represent two related quantities, and K is used to represent their ratio proportional relationship, it can be expressed by the following formula: Y: X = K (certain).

Two related quantities, one changes and the other changes in the opposite direction. If the product of two numbers corresponding to two quantities is certain, 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 their products, the inverse relationship can be expressed by the following formula: xy=k (definite) (k≠0, x≠0).

Proportion:

Proportion is a mathematical term, meaning that two or more formulas are equal. 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. In mathematics, if the change of one variable is always accompanied by the change of another variable, then these two variables are proportional. If these changes are always linked by a constant multiplier, then this constant is called a proportional coefficient or a proportional constant.

Proportion is divided into scale and proportion. The formula that two ratios are equal is called proportion. 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. One of the unknowns in finding the proportion is called the solution ratio.