20以内进位加法和退位减法是整数四则计算的基础。学生是否掌握这部分内容,直接影响着多位数加减法和多位数乘除法能否计算得正确迅速。而入学不久的小学生,初次接触进位、退位,对它既陌生又不容易理解。要突破这一难点,让学生顺利地理解算理,掌握算法,关键的一环是上好20 Carry-in addition and subtraction within 20 is the basis for calculating the integer four. Whether the students master this part of the content directly affects the multi-digit addition and subtraction and multi-digit multiplication and division can be calculated correctly and quickly. The pupil who entered the school not long ago came into contact with the host for the first time and abdicated. It was neither familiar nor easy to understand. To break through this difficulty, let the students understand the arithmetic smoothly, master the algorithm, the key part is to be good 20