Grade 3Math
Adding and Subtracting FractionsCalculating fractions with the same denominator
For fractions with the same denominator, you can add and subtract by thinking about how many base fractions they are made of. Let's look at cases where the answer is up to 1.
The narration and the pictures are in Japanese. You can hear the same words that are used in class at a Japanese school.
- Video
- 1:44（8 scenes）
- Problems
- 2 problems
Open this lesson in Japanese（分数の たし算・ひき算）
Let's try
Write the math sentence in your notebook first, then open the answer.
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1Which is the answer to 3/6 + 2/6: 5/6, 5/12, or 1/6?
Hint
Keep the denominator the same, and add only the numerators.
Answer
It is 5/6. 3 pieces of 1/6 and 2 pieces of 1/6 make 5 pieces of 1/6, so the denominator stays 6, and the numerator becomes 5.
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2Write the answer to 5/8 − 2/8 as a fraction.
Hint
Keep the denominator the same, and subtract only the numerators.
Answer
It is 3/8. Take 2 pieces of 1/8 away from 5 pieces of 1/8, and 3 pieces of 1/8 are left, so the denominator stays 8, and the numerator becomes 3.
Words in this lesson
- denominator 分母
- The bottom number of a fraction. It shows how many equal parts the whole was split into.
- numerator 分子
- The top number of a fraction. It shows how many of those parts there are.
- unit fraction 単位分数
- A fraction whose numerator is 1 (such as 1/5). In addition and subtraction, we think about how many of these there are.
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).
- Thinking of adding and subtracting fractions as "how many of the basic fraction (a fraction whose numerator is 1)" helps prevent the mistake of adding the denominators too (such as getting 2/10 for 1/5 + 1/5). We also recommend folding a paper tape into 5 parts of the same length and coloring them to check.
- On the screen, fractions are written vertically (numerator on top, denominator on the bottom). Calculations whose answers are more than 1 are learned in 4th grade.