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.
Understanding adding fractions with the same denominator
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.
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.
Worked example 2: subtraction
5/6 − 2/6 = ?
Subtract tops: 5 − 2 = 3. Keep the bottom: 6. → 3/6, which simplifies to 1/2.
A common mistake, and the fix
Adding the denominators too.
1/5 + 2/5 is 3/5, not 3/10: the pieces are still fifths, there are just more of them. Only the number of pieces, the top, changes.
Try a few
2/7 + 3/7
3/8 + 3/8
7/10 − 4/10
Try it in Numeris.
A short lesson, then practice with feedback on every answer.
Put the reasoning on paper.
Try six fraction, angle, perimeter and area questions with explained answers, for grades 4–6.
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