Fifth Grade · Math · week 11

Common denominators with models

Find common denominators using multiples and area or fraction-strip models, rewriting fractions as equivalent fractions with the same denominator.

A common denominator is a shared piece size two fractions can both be rewritten with, usually found by using a common multiple of the two denominators.

Fraction-strip or area models make this visible: recut both wholes into the same number of equal pieces, and each original fraction becomes an equivalent fraction with matching pieces.

📋 For the teacher
Teach it (10–15 min):
  • Use fraction strips -- paper strips folded into equal parts -- so recutting the whole is physical, not abstract.
  • List multiples of both denominators side by side and circle the first one they share -- that is the common denominator.
  • Always multiply top AND bottom by the same number, and connect this to multiplying by a fraction equal to 1, like 3/3, so the value never truly changes.
  • Practice with easy pairs first, where one denominator is already a multiple of the other, before moving to harder pairs.
Talk about it:
  • How do you find a common denominator using multiples?
  • Why do you multiply both the top and bottom number by the same amount?
  • Why does 1/2 equal 3/6 even though the numbers look different?

Mastery looks like: They can find a common denominator for two fractions and correctly rewrite each as an equivalent fraction with that denominator.

Common stumbles: Multiplying only the denominator and not the numerator; picking a common multiple that is not actually shared by both denominators.

See it visually

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

FractionsSlice bars and circles into equal parts and compare them.try →MultiplicationEqual groups and arrays make products finally click.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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