1, law of addition, additive commutative law, addition of two numbers, exchange of addend positions, congruence. The law of addition and association, when three numbers are added, you can add the first two numbers and then add the third number. Or add the last two numbers first, and then add the first number, and the sum remains the same. These two laws of addition are often used together.

2, the nature of continuous reduction, a number MINUS two numbers in a row is equal to the sum of this number MINUS those two numbers. 3. Multiplication operation rule, multiplication exchange rule, multiplication of two numbers, the position of exchange factor, and the product remain unchanged. Multiplication and association law, three numbers multiply, you can multiply the first two numbers, then the third number, or you can multiply the last two numbers and then the first number, and the product is unchanged. Multiplication and distribution law, the sum of two numbers multiplied by a number, you can first multiply these two numbers by these two numbers respectively, and then add the products. 4. The nature of continuous division. One number divided by two numbers equals the product of these two numbers.