2. Addition and subtraction within 10,000.

3. Quadrilateral.

4. Division with remainder.

5. Hours, minutes and seconds.

6. Multiply multiple numbers by one number.

7. Preliminary understanding of scores.

8. Possibility.

9. Mathematical wide angle (simple permutation and combination problem).

Add operation

1, add two numbers with the same sign, take the same sign as the addend, and add the absolute values.

2. Add two numbers with different signs. If the absolute values are equal, the sum of two numbers with opposite numbers is 0; If the absolute values are not equal, take the sign of the addend with the larger absolute value and subtract the smaller absolute value from the larger absolute value.

3. Add two numbers with opposite numbers to get 0.

4. Adding a number to 0 still gets this number.

You can add two opposite numbers first.

6. Numbers with the same sign can be added first.

7. Numbers with the same denominator can be added first.