二年级下册数学沪教版千以内数的认识与表达课件(共29张PPT)

(共29张PPT)
千以内数的认识与表达（一）
课前练习:
读出这些数并说数的组成
40是由4个十组成
课前练习:
读出这些数并说数的组成
44是由4个十和4个一组成
课前练习:
读出这些数并说数的组成
50是由5个十组成
课前练习:
读出这些数并说数的组成
100是由10个十或100个一组成
百数图
体育馆A台观看跑步比赛，估计一下看台上有几人？
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千数图
10个百是一千
1000里有10个百
3个百是( )
300
6个百是( )
600
8个百是( )
800
100
100
100
100
100
100
100
100
100
100
1
百位
十位
个位
0
0
2
3
4
5
6
7
8
9
1000
千位上的1，表示
1个千
千位
1
0
五百五百地数 2个500是一千
一百一百地数 10个100是一千
二百二百地数 5个200是一千
在千数图上可以找到1—1000所有的数，想来试试吗？读出这些数，说说数的组成。
342是由3个百，4个十和2个一组成
它表示342
百位 十位 个位
3 4 2
写作：
读作：
342
三百四十二
在千数图上可以找到1—1000所有的数，想来试试吗？读出这些数，说说数的组成。
340是由3个百，4个十和0个一组成
它表示340
写作：
读作：
340
三百四十
百位 十位 个位
3
4
0
在千数图上可以找到1—1000所有的数，想来试试吗？读出这些数，说说数的组成。
304是由3个百，0个十和4个一组成
它表示304
写作：
读作：
304
三百零四
百位 十位 个位
3
0
4
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简图
它表示342。
342由3个百、4个十和2个一组成。
342=300+40+2
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简图
它表示425。
425由 个百、 个十和 个一组成。
425=400+20+5
百位 十位 个位
写作：
读作：
425
四百二十五
4
2
5
4
2
5
1、看图写数。
写作： 写作：
读作： 读作：
百位 十位 个位
百位 十位 个位
2
3
6
236
二百三十六
4
2
0
402
四百零二
4
2
0
420
四百二十
2、想一想:
四百零九写作：（ ），
它是由（ ）个百、（ ）个十、（ ）个一组成的。
409
4
0
画出简图：
9
1、用简图“□— ”来表示下面的数，并读一读、说一说它们由几个“百”、几个“十”、几个“一”组成：
487
102
720
6
487=400+80+7
102=100+0+2
720=700+20+0
读一读下面的数，说说数的组成（书p11）
读一读下面的数，说说数的组成
853由 个百， 个十和 个一组成
八百五十三
853读作：
8
5
3
读一读下面的数，说说数的组成
350由 个百， 个十和 个一组成
三百五十
350读作：
3
5
0
读一读下面的数，说说数的组成
1000由 个千， 个百， 个十和 个一组成
一千
1000读作：
0
0
0
1
读一读下面的数，说说数的组成
803由 个百， 个十和 个一组成
八百零三
803读作：
8
0
3
1、在数位顺序表中，从右边起，第三位是千位。（ ）
辨一辨
2、9个一、2个百合成290。 （ ）
×
×
百位
9个十
209
辨一辨
3、819的最高位上是8，表示8个千。（ ）
4、一个三位数，百位上是4，其他各位上都是0，这个数是400。（ ）
√
×
百
选择题：
1）209读作：（ ）
A．二百九十 B．二百九 C．二百零九
C
2）由5个百，2个十，3个一组成的数是（ ）
A．523 B．532 C．325
A
3）2个百和7个百合成（ ）
A．27 B．900 C．720
B
书P12
（2）将数列继续下去：
② 305，310，315， ……
③ 800，799，798， ……
④ 750，745，740， ……
⑥ 300，400，500， ……
⑦ 880，870，860， ……
+5
+5
320、325、330、335……
-1
-1
797、796、795、794……
-5
-5
735、730、725、720……
600、700、800、900……
+100
+100
850、840、830、820……
-10
-10
独立写数（书P12）
四百二十三
九百九十九
一百零七
七百八十
五百
一千
107为什么十位上写0？780为什么个位上写0？
423
999
107
780
500
1000
拓展练习
体育馆要评选今天的幸运观众，体育馆的叔叔阿姨们已经摇出了三个幸运数字：5、7、0，凡是由这三个幸运数字组成的三位数都是今天的幸运号码，那么今天的幸运号码到底有哪些呢？