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北师大版教材三年级下册有这样一道例题:电影院有21排座位,每排可坐26人,组织500名同学看电影,能坐得下吗?学生大体有以下三种解法:第一种是列出算式21×26算出电影院一共有多少个座位;第二种是把21排想成20排,每排可坐26人想成可坐25人,口算出20×25的结果与500进行比较;第三种是把21排想成20排,每排可坐26人想成可坐30人,口算出20×30的结果与500比较。学生为什么会这样想?估算教学怎样开展才富有成效呢?一加强学生估算意识的培养
Beijing Normal University version of the textbook third grade have such a case: the cinema has 21 rows of seats, each row can sit 26 people, organize 500 students watching movies, sit down? Students generally have the following three solutions: The first Is to list the formula 21 × 26 calculate the total number of seats in the cinema; the second is to think of 20 rows into 20 rows, each row can sit 26 people want to sit 25 people, the mouth of the results of 20 × 25 and 500 The third is to think of 21 rows into 20 rows, each row can sit 26 people want to sit 30 people, the mouth of the results of 20 × 30 compared with 500. Why do students think so? Estimated teaching how to carry out only productive? One to strengthen the cultivation of students’ assessment of consciousness