The first grade is the first year for students to learn mathematics, and it is also the most basic and important year. What students need to learn is also very simple, such as recognizing numbers, writing numbers, simple addition and subtraction, etc. These are very basic and simple. Addition and subtraction within 10 is the basic knowledge of mathematics and the content that students must master. Learning math well is good for them.

First-year students will learn about addition and subtraction in the middle and later stages of their studies, such as addition and subtraction within 10. The first is the simple addition and subtraction, and then the more difficult addition and subtraction. Although it is addition and subtraction, it is all within 10, which is actually very simple.

First, the related properties of subtraction

1, additive commutative law: a+b = b+a.

For example: 8+ 1= 1+8=9

100+2=2+ 100= 102

2. Additive associative law: a+b+c=a+(b+c)

For example: 7+4+1= 7+(4+1) = (7+4)+1=12.

10-5+2=( 10+2)-5=7

The associative law refers to the binary operation on a given set S. If there is an additive associative law a+b+c=(a+b)+c=a+(b+c) or a multiplicative associative law ax(bxc) = (axb)xc in S, the operation is said to satisfy the associative law.