How to use this sheet

  • Have the child list multiples of both denominators and circle the first one they share.
  • Rewrite both fractions with the common denominator on their own line before adding or subtracting.
  • Estimate first with benchmarks: 1/2 + 3/8 is a bit less than 1.

Common mistakes

  • Adding the tops and the bottoms, so 1/2 + 1/3 becomes 2/5. That is less than 1/2: the answer cannot be right.
  • Changing the denominator but not the top number, so 1/2 becomes 1/6. Multiply both by the same number.
  • Using a common denominator that works for one fraction only. Check that both denominators divide it.

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