Grade 3Math
Rules of Multiplication and Multiplying by 0Splitting to calculate, and multiplying by 0 and 10
Multiplication has rules: the answer stays the same if you switch the numbers, or if you split a number and calculate. Using these rules, you can also think about multiplying by 0 and by 10.
The narration and the pictures are in Japanese. You can hear the same words that are used in class at a Japanese school.
- Video
- 1:06（6 scenes）
- Problems
- 3 problems
Open this lesson in Japanese（かけ算の きまりと 0の かけ算）
Let's try
Write the math sentence in your notebook first, then open the answer.
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1Calculate 6 × 12 by splitting 12 into 10 and 2.
Hint
Calculate 6 × 10 and 6 × 2 separately, and add them later.
Answer
It is 72. 6 × 10 = 60, 6 × 2 = 12. 60 + 12 = 72.
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2What are 8 × 0 and 0 × 8?
Hint
In the point game, think about getting 0 balls in the 8-point spot, and getting 8 balls in the 0-point spot.
Answer
Both are 0. Any number times 0, or 0 times any number, is 0.
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3What is 10 × 7?
Hint
Switch the two numbers, and think about what comes next in the 7 times table.
Answer
It is 70. If you switch them, it is the same as 7 × 10. Add 7 to 7 × 9 = 63: 63 + 7 = 70.
Words in this lesson
- number being multiplied かけられる数
- The first number in a multiplication. The 4 in 4 × 6.
- number you multiply by かける数
- The second number in a multiplication. The 6 in 4 × 6.
- rules of multiplication かけ算の きまり
- Things that are true for every multiplication, such as the answer staying the same if you switch the numbers or split a number to calculate.
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).
- The rule of splitting to calculate is the foundation for the column method of multiplication learned later (thinking of 12 × 4 as 10 × 4 and 2 × 4). Laying out marbles or coins and actually splitting them into 2 groups to count makes it easier to feel. In the video we split the number you multiply by, but you can calculate the same way by splitting the number being multiplied.
- Multiplying by 0 is a place where children tend to feel, "There's nothing, so why make a math sentence?" Try turning it into a situation like the point game, "0 balls in the 3-point spot" and "5 balls in the 0-point spot," and check together that both give a score of 0 points.