“万以内数的减法”是义务教育课程标准实验教科书人教版数学三年级上册第二单元教学内容。教材以“美丽的云南”为题,从情境图中引出计算,三个例题相互联系,又互有区别。教师在备课时要考虑两个问题,一是学生“退位减法”掌握的程度;二是本节教材的三个例题各自重点的定位有何区别,从而加强例题教学的目的性。 “Less than one million in addition ” is compulsory education curriculum standard experimental textbook PEP mathematics third grade second unit teaching content. Textbook to “Beautiful Yunnan ” as the title, derived from the situation diagram calculation, the three cases linked to each other, but also different from each other. Teachers should take two questions into account when preparing lessons, one is the degree to which the student “abdicating subtraction ”; the other is the difference between the three key points in the textbook of this section so as to enhance the purpose of the example teaching.