1
00:00:00,040 --> 00:00:04,600
每加侖汽油的價格爲$2.70 問 14.6加侖的汽油

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

3
00:00:08,200 --> 00:00:14,600
因此 有14.6加侖的汽油

4
00:00:14,600 --> 00:00:17,480
每加侖$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
我們只要乘以2.7

7
00:00:25,030 --> 00:00:26,930
這樣比較簡單

8
00:00:26,930 --> 00:00:28,690
我想你們應該知道$2.70

9
00:00:28,690 --> 00:00:32,390
就相當於每加侖2.7美元

10
00:00:32,390 --> 00:00:34,690
因此 把它們相乘

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

12
00:00:37,750 --> 00:00:39,670
當小數相乘時

13
00:00:39,670 --> 00:00:43,010
只要把它們看成整數

14
00:00:43,010 --> 00:00:44,930
算完再考慮小數點

15
00:00:44,930 --> 00:00:49,040
因此 現在 我們可以把這個看成146乘以27

16
00:00:49,040 --> 00:00:50,820
算完再考慮小數點

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等於42

19
00:00:56,690 --> 00:00:58,410
4寫在這

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

21
00:01:02,570 --> 00:01:04,470
3寫在這

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

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

24
00:01:13,160 --> 00:01:15,570
現在 我們看看2

25
00:01:15,570 --> 00:01:18,330
但這個2 至少在考慮小數點之前

26
00:01:18,330 --> 00:01:19,200
實際上是20

27
00:01:19,200 --> 00:01:20,880
因此 這裡要加個0

28
00:01:20,880 --> 00:01:23,730
用同樣的方法

29
00:01:23,730 --> 00:01:25,600
這是一個傳統的乘法問題

30
00:01:25,600 --> 00:01:27,240
先忽略小數點

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

32
00:01:29,670 --> 00:01:31,710
進1 或者說把1重組

33
00:01:31,710 --> 00:01:33,200
可以把這個忽略

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

35
00:01:37,390 --> 00:01:44,700
2乘以1等於2 然後相加

36
00:01:44,700 --> 00:01:47,210
2加0等於2

37
00:01:47,210 --> 00:01:49,160
2加2等於4

38
00:01:49,160 --> 00:01:51,650
0加9等於9

39
00:01:51,650 --> 00:01:54,940
1加2等於3

40
00:01:54,940 --> 00:01:58,700
現在 我們算出了146乘以27等於多少

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

42
00:02:00,770 --> 00:02:03,370
但題目不是146乘以27

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

44
00:02:06,070 --> 00:02:07,700
因此 現在 我們要考慮小數點

45
00:02:07,700 --> 00:02:11,100
我們只要數一下小數點後面有幾位數

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

47
00:02:13,930 --> 00:02:16,500
因此 它們的乘積 小數點後面

48
00:02:16,500 --> 00:02:17,830
有兩位數

49
00:02:17,830 --> 00:02:20,810
因此 1 2 小數點標在這裡

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

51
00:02:25,240 --> 00:02:30,820
需要39.42美元