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エレメンタリーまなびの未来

Grade 3Math

Adding and Subtracting DecimalsThe column method with carrying and borrowing

If you think about how many 0.1s there are, or line up the decimal points in the column method, you can add and subtract decimals. Let's also look at calculations with carrying and borrowing.

The narration and the pictures are in Japanese. You can hear the same words that are used in class at a Japanese school.

Video
1:43（7 scenes）
Problems
2 problems

Open this lesson in Japanese（小数の たし算・ひき算）

0:00
  1. 1Putting water together0:00
  2. 2How many 0.1s0:10
  3. 3Writing the column method0:25
  4. 4Carrying0:39
  5. 5Subtract by counting 0.1s0:56
  6. 6Borrowing1:11
  7. 7Let's try1:30

Let's try

Write the math sentence in your notebook first, then open the answer.

  1. 1Which is the answer to 0.8 + 0.7: 1.5, 0.5, or 15?

    Hint

    If the tenths place becomes 10 or more, put 10 of them together as 1 in the ones place, and write the rest in the tenths place.

    Answer

    It is 1.5. 8 and 7 of 0.1 make 15. 10 of them make 1, so 0.8 + 0.7 = 1.5.

  2. 2Write the answer to 1.4 − 0.6.

    Hint

    If you can't subtract in the tenths place, borrow from the ones place.

    Answer

    It is 0.8. Take 6 of 0.1 away from 14, and 8 are left, so 1.4 − 0.6 = 0.8.

Words in this lesson

decimal point 小数点しょうすうてん
The "." mark in 0.6. In the column method, write the decimal points lined up in a column.
tenths place 小数第一位しょうすうだいいちい
The place to the right of the decimal point. It is also called the 1/10 place (the first decimal place).
carrying / borrowing くり上がり・くり下がりくりあがり・くりさがり
Carrying: when a place has 10 or more, you put 10 of them together as 1 in the place to the left and write the rest in that place. Borrowing: when you can't subtract in a place, you take 1 from the place to the left and make it 10 in that place.

For parents and guardians

  • The names of lessons and the order of topics differ slightly between textbooks. This page follows the content of Japan's national curriculum guidelines (the Course of Study).
  • If you think of adding and subtracting decimals as "how many 0.1s," you can see that it is the same calculation as with whole numbers. In the column method, it is important to line up the decimal points in a column, and the decimal point in the answer also goes in that same lined-up position.
  • In 3rd grade, calculations up to the tenths place (the 1/10 place) are covered.