2 can be decomposed into1+1; 3 can be decomposed into:1+2; 4 can be decomposed into: 1+3 and 2+2; 5 can be decomposed into: 1+4 and 2+3; 6 can be decomposed into: 1+5 and 2+4 and 3+3.

7 can be decomposed into: 1+6 and 2+5 and 3+4; 8 can be decomposed into: 1+7 and 2+6 and 3+5 and 4+4; 9 can be decomposed into: 1+8 and 2+7 and 3+6 and 4+5.

About primary school mathematics:

Primary school mathematics is to teach children a series of knowledge about number, four operations, the calculation formula of figure and length, unit conversion and so on through textbooks, which lays a good mathematical foundation for junior high school and daily life calculation.

Judging from the mathematics learning psychology of primary school students, the learning process of students is not a passive absorption process, but a reconstruction process based on existing knowledge and experience. Therefore, learning while doing and learning while playing will make children learn more actively.