Multiplication formula: factor x factor = product; Product factor = factor. Division formula: dividend-divisor = quotient; Quotient x divisor = dividend; Dividend quotient = divisor. Algorithm of multiplication and division: 1. When operating at the same level, it is calculated from left to right. 2. Two-stage operation, first multiply and then divide, then add and subtract. 3. When there are brackets, count the inside of brackets first, and then count the outside of brackets. 4. When there are multiple brackets, count the brackets first, then the brackets inside, then the braces inside, and finally the brackets outside. Multiplication is a shortcut to add up the same numbers. The result of its operation is called product, and "X" is the symbol of multiplication. The multiplication of integers (including negative numbers), rational numbers (fractions) and real numbers is a systematic summary of this basic definition. Multiplication can also be seen as calculating the objects arranged in a rectangle (integer) or finding the area of a rectangle with a given side length. The area of the rectangle does not depend on which side is measured first, which shows the exchange property. The product of two measured values is a new type of measurement, for example, multiplying the length of two sides of a rectangle to get its area, which is the theme of size analysis. Division is one of the four operations. Given the product of two factors and a non-zero factor, the operation of finding another factor is called division. Division of two numbers is also called the ratio of two numbers. If ab=c(b≠0), the operation of finding another factor A by multiplying the product C and the factor B is division, which is marked as c÷b and pronounced as C divided by B (or B divided by C). Where c is called dividend, b is called divisor, and the result of operation A is called quotient.