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Grade 5 Math · Level 2, Fractions as Numbers

Add & Subtract Fractions with Unlike Denominators

How the lesson starts: Add & Subtract Fractions with Unlike Denominators

1. Wizard Wren's potion

   Wizard Wren is brewing a bubbly potion. The recipe needs 1/3 cup of moon juice and 1/6 cup of star syrup. How much potion is that? The pieces are different sizes, so we need a clever trick!

2. Make the pieces match

   Here is 1/3. Here is 1/6. Different sizes, so we can't just count them. But 6 is a multiple of 3, and 1/3 is the same as 2/6! Now both are sixths. 2/6 + 1/6 = 3/6, which simplifies to 1/2 cup!

3. Subtracting potions

   Wren has 2/3 cup of dragon tea and pours out 5/12 cup. 12 is a multiple of 3, so rewrite 2/3 as twelfths: 3 × 4 = 12, so 2 × 4 = 8. Now 8/12 − 5/12 = 3/12 = 1/4. Watch out: never subtract straight across!