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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Practice adding fractions with the same denominator in Numeris with instant feedback.
Put the reasoning on paper.
Try six fraction, angle, perimeter and area questions with explained answers, for grades 4–6.
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