一、运用加法交换律和结合律进行简便运算例1 (第五册,P.22,6题)282+53+47+18=(282+18)+(53+47)=300+100=400例2 (第七册,P.26,6题)4.36+1.73+0.64+0.27=(4.36+0.64)+(1.73+0.27)=5+2=7教学这类练习题的关键,是引导学生观察哪两个(或几个)加数能凑成和是整十、整百、整千的数。凡能“凑整”的数,其特点是:末尾数字的和是10。分数、小数相加的简算,是凑成整数。两个 First, the use of additive exchange law and the law of combining a simple operation Example 1 (fifth book, P.22, 6 questions) 282 +53 +47 +18 = (282 +18) + (53 +47) = 300 +100 = 400 Case 2 (Book 7, P.26, 6 questions) 4.36 + 1.73 + 0.64 + 0.27 = (4.36 + 0.64) + (1.73 + 0.27) = 5 + 2 = 7 The key to teaching this type of exercise is to guide The student observes which two (or more) addends can make up and is a whole ten, a hundred, a thousand. Where can “round” number, which is characterized by: the sum of the last number is 10. Scores, decimal sum of the simple calculation is to make up an integer. Two