Fourth Grade · Math · week 30

Adding and subtracting like denominators

Add and subtract fractions with the same denominator, simplifying and converting sums greater than 1.

When two fractions share a denominator, the pieces are already the same size, so just add or subtract the numerators and keep the denominator exactly the same. Never add or subtract the denominators themselves.

If the resulting numerator is bigger than the denominator, the answer is more than one whole; convert it to a mixed number. Always check afterward whether the answer can be simplified.

📋 For the teacher
Teach it (10–15 min):
  • Use the same fraction bars or circles from previous weeks; same-size pieces just get counted together.
  • Watch for sums where the numerator passes the denominator, a clear signal to convert to a mixed number.
  • After every answer, check if a number divides evenly into both the top and bottom to simplify.
  • Say out loud every time: "the denominator tells us the size of the piece, and that size does not change."
Talk about it:
  • Why do the denominators stay the same when you add or subtract like fractions?
  • How do you know when a fraction sum needs to become a mixed number?
  • How do you check if a fraction answer can be simplified?

Mastery looks like: They add and subtract fractions with like denominators accurately, converting sums greater than 1 to mixed numbers and simplifying when possible.

Common stumbles: Adding the denominators along with the numerators; forgetting to convert an improper fraction result into a mixed number; leaving an answer unsimplified.

See it visually

Interactive, spoken-aloud tools that show this idea in motion.

FractionsSlice bars and circles into equal parts and compare them.try →SubtractionTake away and count back, step by step.try →AdditionSee groups combine — with counters, blocks, and the number line.try →
Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
Records attendance + 15 min of Math for this learner.
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