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人教版小学数学四年级下“小数的加法和减法”单元例4安排了这样一个情境:四位男生李明、张强、王斌、周刚50米跑的成绩分别是8.42秒、8.46秒、8.54秒、8.58秒。问题是:让他们四人参加4×50米接力赛,可能的总成绩是多少?教材给了两中解法:小莉这样计算:8.42+8.46+8.54+8.58=16.88+8.54+8.58=25.42+8.58=34(秒)小红这样计算:8.42+8.46+8.54+8.58=(8.42+8.58)+(8.46+8.54)=17+17=34(秒)例题的用意很明显,就是要引出整数的运算定律
PEP 4 grade under “addition and subtraction decimal” unit Example 4 arranged such a situation: four boys Li Ming, Zhang Qiang, Wang Bin, Zhou Gang, 50 meters to run the results were 8.42 seconds, 8.46 Sec, 8.54 seconds, 8.58 seconds. The question is: let the four of them participate in the 4 × 50-meter relay race, what is the total score? The textbook gave two solutions: Xiao Li calculated as: 8.42 +8.46 +8.54 +8.58 = 16.88 +8.54 + 8.58 = 25.42 + 8.58 = 34 (seconds) Little Red is calculated as 8.42 + 8.46 + 8.54 + 8.58 = (8.42 + 8.58) + (8.46 + 8.54) = 17 + 17 = 34 (seconds) The purpose of the example is obvious, The law of operation