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2. How to Use Fraction Strips to Add Fractions with Unlike Denominators
Dawn Galente, Arlington CSD 2012
This is a self-paced tutorial. Click the screen each time you want to see the next step.
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3. Fraction strips are models that can be used to show fractions.
1 whole
1/2
1/2
1/3
1/3
1/3
1/4
1/4
1/4
1/4
1/5
1/5
1/5
1/5
1/5
1/6
1/6
1/6
1/6
1/6
1/6
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/12
1/12
1/12
1/12
1/12
1/12
1/12
1/12
1/12
1/12
1/12
1/12

4. How can we add 1/2 + 1/4 using fraction strips?
1. Show 1 whole.
1 whole
2. Use fraction strips to show 1/2 + 1/4.
1 whole
1/2
1/4
3. We need to find fraction strips that can be used to match (that are equivalent to) BOTH the 1/2 and 1/4 lengths. Start by guessing and checking.

5. Can we use thirds to match 1/2 and 1/4?
1 whole
1/2
1/4
1/3
1/3
1/4
1/4
1/4
No- there are no thirds that match (are equivalent to) 1/2.
Can we use fourths to match 1/2 and 1/4?
Yes- 2/4 matches (is equivalent to) 1/2 and 1/4 = 1/4.

6. 1 whole
1/2
1/4
1/4
1/4
1/4
So 1/2 + 1/4 = 3/4.
Let’s try another.

7. How can we add 1/2 + 1/3 using fraction strips?
1. Show 1 whole.
1 whole
2. Use fraction strips to show 1/2 + 1/3.
1 whole
1/2
1/3
3. We need to find fraction strips that can be used to match (that are equivalent to) BOTH the 1/2 and 1/3 lengths. Start by guessing and checking.

8. Can we use thirds to match 1/2 and 1/3?
1 whole
1/2
1/3
1/3
1/4
1/4
1/4
No- there are no thirds that match (are equivalent to) ½.
Can we use fourths to match 1/2 and 1/3?
2/4 is equivalent to 1/2, but there are no fourths that match (are equivalent to) 1/3.

9. 1/2 + 1/3 = 3/6 + 2/6 = 5/6 Can we use sixths to match 1/2 and 1/3?
1 whole
1/2
1/3
1/6
1/6
1/6
1/6
1/6
Yes- 3/6 is equivalent to (matches) 1/2, and 2/6 is equivalent to 1/3.
1/2 + 1/3 =
3/6 +
2/6 =
5/6

10. How can we add 2/3 + 1/4 using fraction strips?
1. Show 1 whole.
1 whole
2. Use fraction strips to show 2/3 + 1/4.
1 whole
1/3
1/3
1/4
3. Find fraction strips that are equivalent to BOTH the 2/3 and 1/4 lengths.

11. Can we use thirds to match 2/3 and 1/4?
1 whole
1/3
1/3
1/4
1/3
1/4
1/4
1/4
No- there are no thirds that are equivalent to 1/4.
Can we use fourths?
No- there are no fourths that are equivalent to 2/3.

12. Can we use sixths to match 2/3 and 1/4?
1 whole
1/3
1/3
1/4
1/6
1/6
1/6
1/6
1/6
No- 4/6 is equivalent to 2/3, but there are no sixths that are equivalent to 1/4.

13. 2/3 + 1/4 = 8/12 + 3/12 = 11/12 What about twelfths? 1 whole 1/3 1/3
Yes- 8/12 is equivalent to 2/3, and 3/12 is equivalent to 1/4.
2/3 + 1/4 =
8/12 +
3/12 =
11/12

14. Have you seen a pattern yet?
Look at the denominators in these problems: 1 2 + 4 = 3 5 6 11 12 8
All of the fraction strips we used were MULTIPLES of both denominators.

15. This is called finding a common denominator- finding the fraction strips that can be equivalent to BOTH denominators.
One fast way to find a common denominator is to multiply both denominators.

16. 1/2 + 2/5 = 5/10 + 4/10= 9/10 Let’s try 1/2 + 2/5. 1 whole 1/2 1/5 1/5
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/10
1/10
Hmmm… if I multiply 2 x 5 I get 10. Can I find tenths that are equivalent to BOTH 1/2 and 2/5?
1/2 + 2/5 =
5/10 +
4/10=
9/10

17. The End