小学数学人教版四年级上《三位数乘两位数》课件(共15张PPT)

(共15张PPT)
三位数乘两位数
小学数学人教版四年级上册
创设情境
一共有多少个点？
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说一说你是怎么计算的？
结合点子图说一说这样算的道理。
创设情境
一共有多少个点？
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14
12
2×14=28
10×14=140
1 4
× 1 2
2 8
1 4 0
1 6 8
2×14=28
10×14=140
28+140=168
14×12=
168
2×14+10×14=168
创设情境
一共有多少个点？
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2×10
10×10
2×4
10×4
10×10=100
10×4=40
2×10=20
2×4=8
100+40+20+8=168
10
2
10
4
创设情境
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14
12
2×14+10×14=168
2×14=28
10×14=140
10
2
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10
2
10
4
2×10
10×10
2×4
10×4
100+40+20+8=168
探究新知
用竖式计算：123×21。
你想到的其他方法是什么？
试一试
在长方形里分一分、画一画，解释这样计算的道理。
1
2
3
探究新知
× 2 1
1 2 3
2 4 6 0 6
2 5 8 3
1×123
20×123
1×123+20×123
123×21=
2583
列竖式计算
1 2 3
123×1
123×20
123
123×1
21
123×20
探究新知
×
2000+400+60+100+20+3=2583
123×21=
2583
100
20
3
20
1
列表格计算
20×100
20×20
20×3
1×100
1×20
1×3
20
1
100
20
3
2000
400
60
100
20
3
探究新知
123×1
123×20
123×1+123×20=2583
100×21
20×21
3×21
100×21+20×21+3×21=2583
20
1
100
20
3
123×21=
2583
列横式计算
探究新知
拆
算
合
把21拆成20和1
把123拆成100、20和3
把21拆成20和1
把123拆成100、20和3
123+2460=2583
123×1=123
123×20=2460
2100+420+63=2583
100×21=2100
20×21=420
3×21=63
2000+400+60+100+20+3=2583
20×100=2000
20×20=400
20×3=60
1×100=100
1×20=20
1×3=3
感悟算理算法
× 1 9
2 4 0 3
2 6 7 0 6
5 0 7 3
9×267
10×267
9×267+10×267
267×19=
5073
2 6 7
尝试用竖式计算
×
2000
200
60
7
10
9
600
70
1800
540
63
尝试用表格计算
2000+600+70+1800+540+63=5073
竖式计算简单又方便，它是表格算法每一步的简化。
从低位乘起，
方便进位书写
巩固练习
课堂小结
今天的学习你有什么收获？
竖式计算
三位数
乘两位数
横式计算
列表格计算
两位数
乘两位数
拆数转化
分别相乘
合并乘积
算理算法
迁移
多位数
乘多位数
迁移
是其它算法
的简化形式
拓展延伸
1画计算方格。
2写因数。
3用乘法口诀计算。
4相加算出算式的积。
4 7 8
4
7
进 1
进 2
进 1
478 × 47 =
“铺地锦”法计算三位数乘两位数
6
6
4
2
2
22466
6
5
2
3
9
4
8
2
8
2
6
1
课后活动
先写一道四位数乘三位数的算式，用学习到的方法计算，并画图解释算理。
例：4356×825=？
再见