1, the law of distribution: If there is a factor that can be multiplied by each item in brackets, then we can assign this factor to each item in brackets. This method can simplify the calculation process and make operation more convenient. For example: 20×(3+4+5)=20×3+20×4+20×5.

2. Law of Association: In addition, if two numbers can be combined, then we can add them first and then add them with other numbers. This method can avoid repeated calculation and improve the calculation speed. For example: (2+3)+(4+5)=2+3+4+5.

3. Extracting common factors: In the multiplication operation, if there are some same factors, then we can extract them. This method can make the calculation simpler and avoid mistakes. For example: 2×3×5=(2×5)×3.

4. Simplification: In fractional operation, if numerator and denominator have common divisor, then we can simplify. This method can make score operation easier and score comparison easier. For example: 4/8=(4/2)/(8/2).

The importance of primary school mathematics;

1. Mastery of basic knowledge: Primary school mathematics is the foundation of mathematics, covering basic knowledge such as counting, basic operation, basic geometry and time measurement. This knowledge is not only necessary for daily life, but also the basis for further study of physics, chemistry and other disciplines.

2. Cultivation of logical thinking: Primary school mathematics is not only calculation and application, but more importantly, it is to cultivate children's logical thinking. By solving math problems, children can learn how to analyze problems, how to reason and how to find solutions.

3. Understanding of mathematical language: Mathematics is also a language, which has its own symbols, formulas and rules. Learning primary school mathematics helps children to understand and master this language, thus playing an important role in more advanced mathematics and science fields.

4. Problem-solving ability: Mathematical problems are often closely related to daily life. Learning primary school mathematics can help children better understand and solve problems in daily life, such as shopping discounts, time management and measurement.