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二 20以內的加减法教材說明本章把20以內的加减法放在一章里教学,主要是为了把下进位的和进位的一位数加法以及相应的减法联系起来教学。为了分散难点,本章又分成下面四部分:1.一位数加一位数(不进位的);2.一位数减一位数;3.一位数加一位数(进位的);4.两位数减一位数(退位的)。由于任何多位数加减法在計算的过程中都要分解成一位数加法和相应的减法,
Addition and Subtraction Less than 20 Explanation of Teaching Materials This chapter addresses the addition and subtraction of up to 20 in a chapter, primarily to teach the teaching of one-digit additions to carry and the corresponding subtraction. In order to disperse the difficulties, this chapter is divided into the following four parts: 1. One digit plus one digit (not carry); 2. One digit minus one digit; 3. One digit plus one digit (carry); 4. Double digits minus one digit (aborted). Because any multi-digit addition and subtraction in the calculation process must be decomposed into one-digit addition and the corresponding subtraction,