1, decimal definition: divide the integer 1 into 10, 100, 1000, and one or more of these parts are decimals, percentages and thousandths, and write them without denominator.

2. Meaning of decimals: decimals consist of integer parts, decimal parts and decimal points. Fractions with denominators of 10, 100, 1000, etc. Can be expressed in decimals.

3. Counting unit: The counting unit of decimals is one tenth, one hundredth and one thousandth. Progressive rate: the progressive rate between every two adjacent counting units is 10, the decimal places are decimals, percentiles and thousandths, and the highest digits are decimals. The lowest bit of the integer part is one bit. The propulsion rate of unit and decile is 10.

4. Basic properties of decimals: Add or remove 0 at the end of decimals, the size of decimals remains unchanged, and only the counting unit of decimals is changed. The movement of decimal position will change the size of decimal. Moving the decimal point to the right will increase the decimal point and moving it to the left will decrease the decimal point.

5. Application of decimals: In real life, the approximate value of decimals is usually chosen, and the method adopted is generally rounding; According to the topic or actual needs, keep two or three decimal places.