Unit 1: decimal multiplication

1, decimal multiplication by integer means the same as integer multiplication, and it is a simple operation to find the sum of several identical addends. For example, 1.2×5 indicates what five 1.2 are.

The significance of multiplying a number by a pure decimal is to find out a few tenths, a few percent and a few thousandths of this number. For example, 1.2×0.5 is five tenths of 1.2.

3. Calculation method of decimal multiplication: To calculate decimal multiplication, first calculate the product by integer multiplication, then look at a factor * * * and how many decimal places it has, count the digits on the right side of the product and point to the decimal point. There are not enough decimal places in the product. You should add 0 in front of it and point to the decimal point.

4. A number (except 0) is multiplied by 1, and the product is equal to the original number.

A number (except 0) is multiplied by a number greater than 1, and the product is greater than the original number.

A number (except 0) is multiplied by a number less than 1, and the product is less than the original number.

5. The commutative law, associative law and distribution rate of integer multiplication are also applicable to fractional multiplication.

Unit 2: Decimal Division

1, fractional division has the same meaning as integer division. It is an operation to find the other factor by knowing the product of two factors and one of them.

For example, 2.4÷ 1.6 means that the product of two known factors is 2.4, and one factor is 1.6, so what is the other factor?

2. Divide the decimal by the integer and divide it by the integer. The decimal point of quotient should be aligned with the decimal point of dividend. If there is a remainder at the end of the division operation, add 0 to continue the division operation.

3. If the dividend is greater than the divisor, the quotient is greater than 1. If the dividend is less than the divisor, the quotient is less than 1.

4. Calculating the divisor is the division of decimals. First, move the decimal point of the divisor to make it an integer. Move the decimal point of the divisor to the right by several digits, and the decimal point of the dividend by several digits. If the number of digits is not enough, add 0 to make up. Then it is calculated by fractional division with the divisor being an integer.

5. When a number (except 0) is divided by 1, the quotient is equal to the original number.

When a number (except 0) is divided by a number greater than 1, the quotient is less than the original number.

When a number (except 0) is divided by a number less than 1, the quotient is greater than the original number.

6.a divided by b = a ÷ b; A divided by b = b ÷ a; A remove b = b ÷ a; A divided by b = a ÷ B

7. The decimal part of a number, starting from a certain number, one or several numbers are repeated in turn. Such decimals are called cyclic decimals.

8. The number of digits in the decimal part is a finite decimal, which is called a finite decimal. Decimals with infinite decimal parts are called infinite decimals. Cyclic decimal is a kind of infinite decimal.

Endless decimal

Decimal cyclic decimal

Endless decimal

Infinite non-repeating decimal

10, the decimal part of a cyclic decimal, and the repeated numbers in turn are called the cyclic segments of this cyclic decimal.

1 1. When writing a cyclic decimal, you can only write the first cyclic segment, and write a cyclic point at the first and last position of this cyclic segment. There are only two circulation points at most.

12, there are three methods to find the divisor: 1, rounding method; 2. Tailing method; 3, into the law. When solving practical problems, according to the actual situation.