① additive commutative law: Two numbers are added, the position of the addend is exchanged, and the sum is unchanged.

a+b=b+a

(2) law of addition and association: when three numbers are added, the first two numbers can be added first, and then the third number can be added; Or add the last two numbers first, and then add the first number, and the sum remains the same.

(a+b) +c=a+(b+c)

Two laws of addition are often used together.

For example:165+93+35 = 93+(165+35)

2. The essence of continuous subtraction: one number subtracts two numbers continuously, which is equal to the sum of this number MINUS those two numbers.

a-b-c=a-(b+c)

3, the law of multiplication:

① Multiplication and exchange law: when two numbers are multiplied, the position of exchange factor remains unchanged.

a×b=b×a

② Multiplication and association law: When three numbers are multiplied, you can multiply the first two numbers and then the third number, or you can multiply the last two numbers and then the first number, and the product remains unchanged.

(a×b) ×c=a×(b×c)

These two multiplication laws are often used in combination.

Such as: 125×78×8.

③ Multiplication and distribution law: When the sum of two numbers is multiplied by a number, the two numbers can be multiplied by these two numbers respectively, and then the products can be added.

(a+b) ×c=a×c+b×c

4. The nature of continuous division: one number divided by two numbers equals the product of these two numbers.

a÷b÷c=a÷(b×c)

Extended data:

The calculation rule of multiplying a number by an integer: the product of the multiplication of an integer and a molecule is a numerator, and the denominator remains unchanged.

Fraction multiplied by fraction: the product of numerator multiplied by numerator is numerator, and the product of denominator multiplied by denominator is denominator.

The calculation rule of fractional division: dividing by a number that is not 0 is equal to multiplying the reciprocal of this number.

Significance of Fractional Multiplication: The significance of Fractional Multiplication is the same as that of Integer Multiplication, which is a simple operation to find the sum of several identical addends.

Significance of Fraction Multiplying Fraction: Find the fraction of a number.

The basic nature of the fraction: the numerator and denominator of the fraction are multiplied or divided by the same number (except 0) at the same time, and the size of the fraction remains unchanged.

Basic properties of decimals: Add "0" or remove "0" at the end of decimals, and the size of decimals remains unchanged.

Baidu Encyclopedia-Operating Rules