A, decimal multiplication:

1, decimal times integer.

2. Approximate value of product (rounding) Multiply, add and subtract.

3. Integer multiplication is extended to decimals (commutative law, distributive law and associative law).

Second, the fractional division:

1, decimal divided by integer.

2, the divisor quotient (rounded, pay attention to the actual situation in the application problem).

Specifically:

Due to the need of counting, human beings abstract natural numbers from physical objects, which is the starting point of all "numbers" in mathematics. Natural number does not close subtraction. For closed subtraction, we extend the number system to integers.

In order not to close division, but to close division, we extend the number system to rational numbers; For open root operation, we extend the number system to algebraic number (in fact, algebraic number is a broader concept).