1, 99 multiplication table: 99 multiplication table is the basic part of primary school learning, the thing that the first-year primary school students contact the most, and the most basic knowledge part in primary school life, so the 99 multiplication table in Grade One is the focus and center of the whole study. In the second grade of primary school, these key points and centers will be reviewed again, and then extended to some commonly used addition and subtraction.

2. Multiplicative commutative law: Then there is the multiplicative commutative law of grade three, which is a calculation law. Mainly talking about the multiplication of two numbers and the exchange of factor positions, the cross product between them is constant. This is called multiplicative commutative law, which can be expressed as: a×b=b×a, the two exchange positions, but the product remains the same, so it can be calculated from left to right in normal order!

3. Lines, angles, natural numbers and integers: line segments and angles are easier to understand. A line segment refers to a limited part between two points on a straight line, including two endpoints. An angle mainly refers to two suspected collection objects with a common endpoint, which is called an angle. Natural numbers are numbers that measure things or indicate the number of times and pieces of things. Integers are numbers that indicate the number of objects, called integers, and 0 means nothing, so 0 is also an integer.

4. Fraction, decimal and division: Fraction refers to dividing a part of the original whole into any equal parts, and decimal is a special representation of real numbers. All fractions can be expressed as decimals, and then division is one of the four operations.

5. Percent and probability: Percent is a special fraction, and the denominator is 100. This numerator may not be an integer. Probability is a statistical term, which is mainly used to reflect the possibility of random events.