1
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每加仑汽油的价格为$2.70 问 14.6加仑的汽油

2
00:00:04,600 --> 00:00:08,200
需要多少钱？

3
00:00:08,200 --> 00:00:14,600
因此 有14.6加仑的汽油

4
00:00:14,600 --> 00:00:17,480
每加仑$2.7

5
00:00:17,480 --> 00:00:21,330
或者可以把$2.70看成2.7美元

6
00:00:21,330 --> 00:00:25,030
我们只要乘以2.7

7
00:00:25,030 --> 00:00:26,930
这样比较简单

8
00:00:26,930 --> 00:00:28,690
我想你们应该知道$2.70

9
00:00:28,690 --> 00:00:32,390
就相当于每加仑2.7美元

10
00:00:32,390 --> 00:00:34,690
因此 把它们相乘

11
00:00:34,690 --> 00:00:37,750
因此 首先我们要…提醒一下

12
00:00:37,750 --> 00:00:39,670
当小数相乘时

13
00:00:39,670 --> 00:00:43,010
只要把它们看成整数

14
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算完再考虑小数点

15
00:00:44,930 --> 00:00:49,040
因此 现在 我们可以把这个看成146乘以27

16
00:00:49,040 --> 00:00:50,820
算完再考虑小数点

17
00:00:50,820 --> 00:00:53,330
因此 首先是7乘以6

18
00:00:53,330 --> 00:00:56,690
7乘以6等于42

19
00:00:56,690 --> 00:00:58,410
4写在这

20
00:00:58,410 --> 00:01:02,570
7乘以4等于28 加4等于32

21
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3写在这

22
00:01:04,470 --> 00:01:08,450
7乘以1等于7 加3等于10

23
00:01:08,450 --> 00:01:13,160
得到7乘以146等于1022

24
00:01:13,160 --> 00:01:15,570
现在 我们看看2

25
00:01:15,570 --> 00:01:18,330
但这个2 至少在考虑小数点之前

26
00:01:18,330 --> 00:01:19,200
实际上是20

27
00:01:19,200 --> 00:01:20,880
因此 这里要加个0

28
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用同样的方法

29
00:01:23,730 --> 00:01:25,600
这是一个传统的乘法问题

30
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先忽略小数点

31
00:01:27,240 --> 00:01:29,670
2乘以6等于12

32
00:01:29,670 --> 00:01:31,710
进1 或者说把1重组

33
00:01:31,710 --> 00:01:33,200
可以把这个忽略

34
00:01:33,200 --> 00:01:37,390
2乘以4等于8 加1等于9

35
00:01:37,390 --> 00:01:44,700
2乘以1等于2 然后相加

36
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2加0等于2

37
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2加2等于4

38
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0加9等于9

39
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1加2等于3

40
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现在 我们算出了146乘以27等于多少

41
00:01:58,700 --> 00:02:00,770
等于3942

42
00:02:00,770 --> 00:02:03,370
但题目不是146乘以27

43
00:02:03,370 --> 00:02:06,070
而是14.6乘以2.7

44
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因此 现在 我们要考虑小数点

45
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我们只要数一下小数点后面有几位数

46
00:02:11,100 --> 00:02:13,930
这有1位 这有2位

47
00:02:13,930 --> 00:02:16,500
因此 它们的乘积 小数点后面

48
00:02:16,500 --> 00:02:17,830
有两位数

49
00:02:17,830 --> 00:02:20,810
因此 1 2 小数点标在这里

50
00:02:20,810 --> 00:02:25,240
因此 每加仑汽油2.7美元 14.6加仑

51
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需要39.42美元