(西师大版)四年级数学上册教案多位数加减法的估算.pdf

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1、多位数加减法的估算教学目标：知识与能力：结合具体情景，让学生利用已有的知识经验估算整万数加减法。过程与方法：体会估算方法的多样化。情感态度价值观：初步培养学生迁移的学习能力。教学重难点：初步学会用迁移的方法探索多位数加减法的口算方法，并能较为熟练地进行口算。教具学具准备：多媒体课件或教学挂图。教学过程：一、情景引入，提出问题教师：有个四年级的小学生明明，上网查到了这样一条信息。出示例 2 主题图。教师：你们知道是一条怎样的信息吗？学生：明明查到了2001 年某地退耕还林 401535公顷，2002年达 2039800公顷。教师：如果你是明明，你能根据这条信息提出问题吗？思考以后，同桌的两个小朋

2、友先交流交流。同桌互动。教师：谁来发表想法？学生 1：两年一共退耕还林大约多少公顷？学生 2：2002 年退耕还林比 2001 年大约多多少公顷？教师：能对他们提出的问题进行列式计算吗？学生：能，算式分别是2039800+401535和 2039800-401535。（教师板书算式）二、引导释疑，探究方法教师：刚才有个同学的提问中用到了“大约”二字，在这里你为什么要使用“大约”呢？学生 1：因为这道题的数目太大，计算会比较麻烦，我用“大约”的意思就是希望对结果进行大概的计算，不要求很精确。学生 2：我认为他用“大约”就是要我们对结果进行估算。教师：同学们的想法很正确，在实际生活中，我们经常对这

3、些较大数目加减法的计算结果要求不是那么精确，可以对它进行估算，今天我们就要学习多位数加减法的估算。039800401535”为例，能估算出这道题的结果吗？四人一组，说一说你是怎样估算的？小组探究。教师：谁来汇报汇报？学生 1：我用“四舍五入”法，把2039800看作 204 万，把 401535看作 40 万，再用 204 万一 40 万，结果大约就是 164 万。文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T

4、1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 H

5、U3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A

6、3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码

7、:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10

8、B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3

9、ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H1

10、0G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9学生 2：老师，我的方法更简便，我把2039800看作 200万，把 401535仍然看作40 万，200 万-40 万，结果大约就是160万。教师小结：真是聪明的孩子，敢于思考，并且善于思考。大家通过讨论，

11、已经找到了多位数加减法的估算方法，我们通常就是把两个数看作整万的数，然后再进行加减。三、尝试运用，巩固提高1.教师：掌握了估算方法，能很快估算出2039800401535的结果吗？说一说你是怎样想的？学生 1：200 万+40万，结果大约是 240 万。2.完成第 35 页的课堂活动。点评：例题以退耕还林中的数学问题为题材，体现了内容的现实性，让学生在学习数学的同时，也关注社会的发展。通过儿童在网上查阅资料的情境呈现信息，有利于让学生对例题的学习产生亲近感。多位数加减法的估算以求近似数、整十整百数加减法口算为认知基础，由教师引导学生通过课堂活动自主探究，充分体现了让学生利用已有知识进步 文档编

12、码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I1

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18、9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7N6I10B3P9文档编码:CL10G7A3S10N1 HU3H10G4T1D3 ZC7

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