The decomposition and combination of 2 and 3 is 2, which can be divided into 1 and 1, and the combination of 1 and 1 is 2. 3 can be divided into 1 and 2, 1 and 2, which add up to 3. 3 can also be divided into 2 and 1, and the combination of 2 and 1 is 3.

The decomposition and combination of numbers is actually a test of everyone's initial understanding of mathematical thinking ability. A number is divided into two parts through situational sensory cognition and deep understanding. The decomposition and synthesis of numbers is actually the predecessor of the understanding and calculation of addition and subtraction in mathematics.

Introduction to decomposition and synthesis

The structure of pre-school mathematics special exercises: decomposition and synthesis, integrating the knowledge of pre-school children; Give priority to practice and combine practice with teaching; Strengthen ability training. Let children learn the decomposition and synthesis of numbers within 20. Pre-school Mathematics Exercise: Decomposition and Composition is compiled by Chenxi Early Childhood Education Development Center according to the Guiding Outline of Kindergarten Education (Trial) issued by the Ministry of Education.

In the process of decomposition and combination, we will find that when a right side is added to the left, there will be duplication in the process of reducing one. For example, four can be decomposed into one and three or four, and can also be decomposed into three and one. This way, in fact, is repetitive, and they get the same result twice. This can also be more deeply understood as the law of exchange.

Baidu Encyclopedia-Decomposition and Synthesis