First, the law of addition:

1, additive commutative law: Two numbers are added, the addend positions are exchanged, and the sum is unchanged. a+b=b+a .

2, the law of addition and association: three numbers are added, you can add the first two numbers first, 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. (a+b)+c=a+(b+c).

These two laws of addition are often used together.

For example:165+93+35 = 93+(165+35) What is the basis?

3. 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).

Second, the law of multiplication:

1, multiplication method of substitution: When two numbers are multiplied, the exchange factor position 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: the sum of two numbers is multiplied by one number. You can multiply these two numbers with this number first, and then add the products, for example, (a+b)×c=a×c+b×c, (a-b) × c = a× c-b× c.