3.18十进制减法

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  十进制减法

  

  [Figure 1]

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  Ivana goes to the thrift store with $20 in her pocket. She purchases a shirt and a necklace that total $12.42. Ivana hands the cashier her $20 bill and watches as the cashier enters the number. Ivana tries to predict the  amount  of change that she will receive from the cashier, but she can't decide what to do since $12.42 and $20 have a different number of digits. Can you find the  difference  between $20 and $12.42 and figure out much change the cashier should give Ivana?
  ::伊万娜在口袋里拿着20美元去利夫特商店。她买了一件衬衫和一条项链,总共12.42美元。 伊万娜把出纳员的20美元钞票和手表交给出纳员,当出纳员进入号码时。 伊万娜试图预测她从出纳员那里会收到多少变化,但她无法决定从12.42美元到20美元以后做什么,数字不同。你能发现20美元到12.42美元的差额,并找出出纳员应该给伊凡娜多少变化吗?

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  In this concept, you will learn how to subtract decimals.
  
  ::在此概念中,您将学会如何减去小数点。

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  Subtracting Decimals
  ::减减十进制

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  To subtract decimals, you will work with the wholes and parts of the numbers separately. First, you subtract the parts and then you subtract the wholes. The best way to do this is to keep the parts together and keep the wholes together. To do this, simply line up the decimal points in each number that you are subtracting.
  ::要减去小数点,您将分别处理数字的整数和部分。首先,您将各部分减为零,然后将整数减为零。最好的办法就是将各部分放在一起,把整数放在一起。要做到这一点,只需将每个减为零的数的小数点排成一行。

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  Let's look at an example.
  ::让我们举个例子。

  6.78 - 2.31 = _____

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  First, line up the problem vertically.
  ::首先,垂直排列问题。

  $$\begin{array}{r}6.78\\ \underset{\_}{-2.31}\end{array}$$

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  Then, subtract each digit vertically.
  ::然后垂直减去每个数字。

  $$\begin{array}{r}6.78\\ \underset{\_}{-2.31}\\ 4.47\end{array}$$

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  The answer is 4.47.
  ::答案是4.47。

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  Sometimes, the values in a subtraction problem can have a different number of digits. Add zeros to help hold places where there are no digits. That way each number has the same number of places.
  ::有时减法问题中的数值可能有不同的位数。 添加零来帮助持有没有位数的位置。 这样每个数字就有相同的位数 。

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  Let's look at an example.
  ::让我们举个例子。

  67.89 - 18.4 = _____

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  First, line up the problem vertically with the  decimal point .
  ::首先,将问题垂直排列在小数点上。

  $$\begin{array}{r}67.89\\ \underset{\_}{-18.40}\\ 49.49\end{array}$$

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  Then, subtract each digit vertically.
  ::然后垂直减去每个数字。

  49.49

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  The answer is 49.49.
  
  ::答案是49.49

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  Examples
  ::实例

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  Example 1
  ::例1

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  Earlier, you were given a problem about Ivana and her purchases at the thrift store.
  ::早些时候,你得到一个问题 伊万娜和她的购买 在节食店。

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  She has $20 and she spends $12.42. How can she subtract her total and calculate her change?
  ::她有20美元,她花12.42美元,她怎么可以扣除总额,计算零钱?

  $$\begin{array}{r}\$20-12.42\end{array}$$

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  First, add zeros to the 20 so that both numbers have the same number of places.
  ::首先,在20个中加上零,这样两个数字的位数相同。

  $$\begin{array}{r}20.00\end{array}$$

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  Next, line up the numbers vertically.
  ::接下来,垂直排列数字。

  $$\begin{array}{r}20.00\\ \underset{\_}{-12.42}\end{array}$$

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  Then, subtract the numbers
  ::然后,减去数字

  $$\begin{array}{r}7.58\end{array}$$

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  The answer is $7.58. Ivana should receive $7.58 from the cashier.
  ::答案是7.58 伊万娜应该从出纳处得到7.58美元

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  Example 2
  ::例2

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  Subtract the decimals.
  ::减去小数。

  12.5 - 10.38 = _____

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  First, add a  zero  to the 12.5 so that both numbers have the same number of places.
  ::首先,在12.5中加上零,这样两个数字的位数相同。

  $$\begin{array}{r}12.5\end{array}$$

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  Next, line up the numbers vertically.
  ::接下来,垂直排列数字。

  $$\begin{array}{r}12.50\\ \underset{\_}{-10.38}\end{array}$$

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  Then, subtract the numbers.
  ::然后,减去数字。

  $$\begin{array}{r}2.12\end{array}$$

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  The answer is 2.12.
  ::答案是2.12。

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  Example 3
  ::例3

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  Subtract the decimals.
  ::减去小数。

  16 - 12.22 = _____

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  First, add zeros to the 16 so that both numbers have the same number of places.
  ::首先,在16个中增加零,这样两个数字的位数相同。

  $$\begin{array}{r}16.00\end{array}$$

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  Next, line up the numbers vertically.
  ::接下来,垂直排列数字。

  $$\begin{array}{r}16.00\\ \underset{\_}{-12.22}\end{array}$$

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  Then, subtract the numbers
  ::然后,减去数字

  $$\begin{array}{r}3.78\end{array}$$

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  The answer is 3.78.
  ::答案是3.78

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  Example 4
  ::例4

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  Subtract the decimals.
  ::减去小数。

  18.86 - 13.45 = _____

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  First, line up the numbers vertically.
  ::首先,垂直排列数字。

  $$\begin{array}{r}18.86\\ \underset{\_}{-13.45}\end{array}$$

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  Then, subtract the numbers.
  ::然后,减去数字。

  $$\begin{array}{r}5.41\end{array}$$

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  The answer is 5.41
  ::答案是5.41

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  Example 5
  ::例5

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  Subtract the decimals.
  ::减去小数。

  19.2 - 13.211 = _____

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  First, add zeros to the 19.2 so that both numbers have the same number of places.
  ::首先,在19.2中增加零,这样两个数字的位数相同。

  $$\begin{array}{r}19.200\end{array}$$

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  Next, line up the numbers vertically.
  ::接下来,垂直排列数字。

  $$\begin{array}{r}19.200\\ \underset{\_}{-13.211}\end{array}$$

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  Then, subtract the numbers.
  ::然后,减去数字。

  $$\begin{array}{r}5.989\end{array}$$

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  The answer is 5.989.
  ::答案是5.989。

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  Review
  ::回顾

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  Subtract the following decimals.
  ::减去以下小数。

  1. 17.65 - 4 = _____
  2. 18.97 - 3.4 = _____
  3. 22.50 - .78 = _____
  4. 27.99 - 1.99 = _____
  5. 33.11 - 3.4 = _____
  6. 44.59 - 11.34 = _____
  7. 78.89 - 5 = _____
  8. 222.56 - 11.2 = _____
  9. 567.09 - 23.4 = _____
  10. 657.80 - 3.04 = _____
  11. 345.01 - 123.90 = _____
  12. 567.08 - 111.89 = _____
  13. 378.99 - 345.12 = _____
  14. 786.01 - 123.10 = _____
  15. 504.32 - 345.89 = _____

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  Review (Answers) 
  ::回顾(答复)

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  Click   to see the answer key or go to the Table of Contents and click on the Answer Key under the 'Other Versions' option.
  ::单击可查看答题键, 或转到目录中, 单击“ 其他版本” 选项下的答题键 。

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  Resources
  ::资源