Adding and Subtracting Like Fractions
Aligned to 4.NF.B.3 — Common Core State Standards for Mathematics.
What this lesson teaches
A fraction like 5/8 is just five copies of the unit fraction 1/8 added together. When denominators are the same, add or subtract the numerators and keep the denominator the same.
Worked examples
Example 1
2/8 + 3/8. Both are eighths, so add the numerators: 2 + 3 = 5, keep the denominator 8. Answer: 5/8. You can see it as 1/8 + 1/8 + 1/8 + 1/8 + 1/8 = 5/8.
Example 2
7/10 − 4/10. Both are tenths, so subtract the numerators: 7 − 4 = 3. Answer: 3/10.
Example 3
Only the numerators change. 2/8 + 3/8 is 5/8, not 5/16 — the pieces stay the same size, you just have more of them.
Practice questions
- Add: 3/6 + 2/6.
- Subtract: 7/10 - 4/10.
- Write 4/5 as a sum of unit fractions, then find 4/5 - 1/5.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Sumar y restar fracciones iguales
Una fracción como 5/8 es solo cinco copias de la fracción unitaria 1/8 sumadas. Cuando los denominadores son iguales, suma o resta los numeradores y deja el denominador igual.
Ejemplo 1: 2/8 + 3/8. Ambas son octavos, así que suma los numeradores: 2 + 3 = 5 y deja el denominador 8. Respuesta: 5/8. Lo puedes ver como 1/8 + 1/8 + 1/8 + 1/8 + 1/8 = 5/8.
Ejemplo 2: 7/10 − 4/10. Las dos son décimos, así que resta los numeradores: 7 − 4 = 3. Respuesta: 3/10.
Ejemplo 3: Solo cambian los numeradores. 2/8 + 3/8 es 5/8, no 5/16 — las partes siguen del mismo tamaño, solo tienes más.
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