- We will represent and solve addition and subtraction of fractions with unequal denominators.
- I will use fraction strips to model addition and subtraction of fractions with unequal denominators.
Whole Class Lesson
I began by having my students add a fraction strip diagram to their math journal.
I demonstrated how to use the fraction strip to find equivalent fractions using a ruler. We lined up the ruler with 1/2 and determined that 2/4, 3/5, 4/8, 5/10, and 6/12 were all equivalent. We repeated this with 1/4, 2/3, 3/5, etc.
Once we had become comfortable with finding equivalents (more or less), we started adding and subtracting fractions with unlike denominators.
I have them the problem 1/2 + 1/4
- First I demonstrated how to use the ruler to find the fractions that were equal to 1/2. We rediscovered that 1/2 shares a common denominator with 1/4s.
- We determined that we would change 1/2 to 2/4 (equivalent fraction) and then we could add.
We continued this process using our fraction strip table to help us find common denominators. Then we used our common denominator to help us create equivalent fractions. Finally, we were able to add or subtract.
When we located a problem that required us to change both fractions in order to find a common denominator, I exposed them to the "butterfly" method.
We did discover that using the butterfly method could mean that we need to simplify our fraction.