20以内的退位减法同20以内的进位加法一样，是学生学习数学重要基础，也是低年级教学的重点。教学时，要注意以下六点。1沟通加减法之间的联系。20以内退位减法教学的基础是20以内的进位加法。因为退位减法的计n要凭借Zn以内的进位加法来思考。即“想加勇减”。因此，要突出加 Less than 20 abatement subtraction with carry within 20 plus, is an important foundation for students to learn mathematics, but also the focus of the lower grade teaching. When teaching, pay attention to the following six points. 1 communication between the addition and subtraction of the link. Less than 20 abatement subtraction teaching is based on the carry within 20 addition. Because the abatement subtraction method, n, depends on the carry addition within Zn. That is, “want to add brave”. Therefore, to highlight Canada