Adding Fractions with the Same Denominator (Grade 4)
When two fractions have the same denominator, the pieces are already the same size — so adding them is just counting pieces. Add the top numbers (how many pieces), and keep the bottom number the same (the size of each piece doesn't change). 1/5 + 2/5 means "one fifth-piece plus two fifth-pieces" = three fifth-pieces = 3/5.
Understanding adding fractions with the same denominator
When two fractions have the same denominator, the pieces are already the same size — so adding them is just counting pieces. Add the top numbers (how many pieces), and keep the bottom number the same (the size of each piece doesn't change). 1/5 + 2/5 means "one fifth-piece plus two fifth-pieces" = three fifth-pieces = 3/5.
A common slip to avoid: do not add the denominators. 1/5 + 2/5 is 3/5, never 3/10 — the pieces didn't get smaller, you just have more of them. Subtraction works the same way: subtract the tops, keep the bottom.
Key Idea
A common slip to avoid: do not add the denominators. 1/5 + 2/5 is 3/5, never 3/10 — the pieces didn't get smaller, you just have more of them. Subtraction works the same way: subtract the tops, keep the bottom.
Seeing it in action
Worked example
1/5 + 2/5 = ?
Same denominator (fifths). Add tops: 1 + 2 = 3. Keep the bottom: 5. → 3/5. (Visual: a bar in fifths, light 1 piece then 2 more = 3 shaded.)
Worked example 2: subtraction
5/6 − 2/6 = ?
Subtract tops: 5 − 2 = 3. Keep the bottom: 6. → 3/6, which simplifies to 1/2.
Try a few
2/7 + 3/7
3/8 + 3/8
7/10 − 4/10
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