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Adding fractions with unlike denominators
You can only add fractions directly when the pieces are the same size. So the job is to rewrite both fractions with a common denominator first. This is usually a 5th grade skill, and it depends on equivalent fractions and multiplication facts.
Three steps, with examples
- 1/4 + 2/3. Step 1: find a common denominator. 12 works, because 4 and 3 both go into 12. Step 2: rewrite. 1/4 = 3/12 and 2/3 = 8/12. Step 3: add the tops. 3/12 + 8/12 = 11/12.
- 1/2 + 3/10: 10 is already a multiple of 2, so 1/2 = 5/10 and 5/10 + 3/10 = 8/10 = 4/5.
- 2/3 + 3/4: 8/12 + 9/12 = 17/12 = 1 5/12.
6 practice questions (answers simplified)
- 1/2 + 1/3 = ?
- 1/4 + 3/8 = ?
- 2/5 + 1/10 = ?
- 1/3 + 1/6 = ?
- 3/4 + 1/6 = ?
- 2/3 + 2/5 = 16/15 = ?
Show answers
- 1/2 + 1/3 = 5/6
- 1/4 + 3/8 = 5/8
- 2/5 + 1/10 = 1/2
- 1/3 + 1/6 = 1/2
- 3/4 + 1/6 = 11/12
- 2/3 + 2/5 = 16/15 = 1 1/15
Tips for parents
- Multiplying the two denominators always gives a common denominator, but a smaller one is easier.
- Simplify at the end and turn improper answers into mixed numbers.
- If this step is shaky, check equivalent fractions first.