Additive commutative law: When two numbers are added, the positions of the addends are reversed, and their sum remains the same. That is, a+b = b+a;
Law of addition and association: when three numbers are added, the first two numbers are added first, and then the third number is added; Or add the last two numbers first, and then add the first number, and their sum remains the same.
These two addition algorithms can be extended to the addition of any number.
Therefore, the calculation method of multi-digit addition is: align with the same digit, starting with one digit.
Multiplication and exchange law: when two numbers are multiplied, the position of the exchange factor remains unchanged.
Multiplication and association law: multiply three numbers, first multiply the first two numbers, and then multiply the third number; Or multiply the last two numbers first, and then multiply them with the first number, and their products remain unchanged.
Multiplication and distribution law: when the sum of two numbers is multiplied by a number, you can multiply the two addends by this number respectively, and then add the two products, and the result remains unchanged.
Multiplicative commutative law and associative law can be extended to the multiplication of multiple numbers. The law of multiplication and distribution can be extended not only to the case of multiple addends, but also to the case that the difference between two numbers is multiplied by one number.
According to the extended multiplication and division method, the calculation rules of multiple digits multiplied by one digit and multiple digits multiplied by multiple digits are obtained.