The composition of numbers, also known as the combination of numbers, means that a number (total) can be divided into several parts, and several parts can be combined into a number (total). For children, the composition of numbers only refers to the combination of a number and two parts.

The composition of numbers is of great significance in mathematics, which reflects the substantive relationship of numbers.

The relationship between numbers (equivalence, complementarity and exchange)

Through the composition and decomposition of numbers, children must master knowledge points;

Equivalence relation: the total can be divided into two parts which are equal or unequal, but the sum of the two parts is equal to the total, which is the equivalence relation between the total and the parts. Complementarity: under the condition of constant total, one part decreases and the other part increases, which is the complementarity between parts. Interchange relationship: the exchange position of the two parts, the sum of which remains unchanged, is the exchange relationship of the two parts.

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