Lesson: Addition of Fractions with Like Denominators

Purpose: You will use Fraction Island models on the geoboard to find sums of fractions with like denominators.

Materials:

• A set of fraction islands and a geoboard shared with a partner

• Fraction island sheet

• Colored Pencils

• Pencil

Investigation:

1. Make two 2X7 units on the geoboard

   1. Model 1/7 in one of the units

   2. Model 3/7 in the other unit

   3. Put all four of the red islands in one of the units and decide what number is modeled

   4. Draw a picture of the model on your Fraction Island sheet

   5. Write by your picture the equation: 1/7 + 3/7 = 4/7

2. Make two 3X3 units on the geoboard

   1. Model 5/9 in one of the units

   2. Model 2/9 in the other unit

   3. Put both sets of yellow islands in one of the units to find the sum of 2/9 and 5/9

   4. Draw a picture of the model

   5. Write by your picture the equation: 5/9 + 2/9 = 7/9

3. Make one 3X5 unit on the geoboard

   1. Model both 3/5 and 1/5 to find the sum of the two fractions

   2. Make a drawing of your model

   3. Write beside your picture the equation: 3/5 + 1/5 = 4/5

4. For each of the following, decide what size islands to use, make the model, find the sum, and write the matching addition equation:

   1. 2/4 + 1/4 on a 4X4 unit

   2. 4/10 + 3/10 on a 2X5 unit

   3. 1/3 + 2/3 on a 3X5 unit