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エレメンタリーまなびの未来

Grade 3Math

Multiplying by 2-Digit Numbers in ColumnsCarrying, and writing shifted over

In the column method where the number you multiply by has 2 digits, you multiply by the ones digit and the tens digit separately, then add the two answers with the places shifted.

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

Video
2:31（9 scenes）
Problems
2 problems

Open this lesson in Japanese（2けたを かける 筆算）

0:00
  1. 1Multiplying by a 2-digit number0:00
  2. 2Multiply by the ones digit0:12
  3. 3Multiply by the tens digit0:29
  4. 4Add to get the answer0:46
  5. 5Numbers with a hundreds place1:02
  6. 6Multiply by the tens digit and add1:21
  7. 7A 0 in the number you multiply by1:39
  8. 8Check with an estimate1:56
  9. 9Let's try2:14

Let's try

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

  1. 1Calculate 54 × 23 with the column method.

    Hint

    First multiply by the ones digit, then multiply by the tens digit and shift it one place to the left.

    Answer

    It is 1242. 54 × 3 = 162. 54 × 2 = 108, shifted one place to the left (1080). 162 + 1080 = 1242.

  2. 2Calculate 135 × 24 with the column method.

    Hint

    Numbers with a hundreds place work the same way if you multiply in order from the ones place.

    Answer

    It is 3240. 135 × 4 = 540. 135 × 2 = 270, shifted one place to the left (2700). 540 + 2700 = 3240.

Words in this lesson

column method 筆算ひっさん
A way of calculating where you write the numbers with their places lined up in columns.
partial products 部分の 積ぶぶんのせき
The answers you get when you split the number you multiply by into its ones digit and tens digit and multiply by each.
estimate 見積もりみつもり
Changing numbers to friendly numbers to find an answer that is about right.

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).
  • Children often stumble on writing the second answer shifted one place to the left. Explaining it with an example like 36 × 20 = 720, "because you are multiplying by the tens digit, it is really a number 10 times as big," makes it easier to understand.
  • An easy way to check whether the answer is right is to see that it is not far off from an estimate. Try changing the 2-digit numbers to friendly numbers and calculating in your head.