Education Technology

Fractions / Adding and Subtracting Fractions with Like Denominators

Grade Level 3,4,5
Activity 5 of 15
This lesson uses interactive number lines to investigate addition and subtraction of fractions that refer to the same whole (i.e. have the same denominator).

Planning and Resources

Students should understand and explain that if two fractions represent the same whole and have the same denominator, their sum is represented by joining end to end the segment of length for one fraction to the segment of the length represented by the second.

properties of addition

Standard: Search Standards Alignment


Lesson Snapshot


As students observe what is happening in this file, help them focus on how subtraction is represented on the number line.

What to look for

Have students illustrate the subtraction on number lines they have drawn. Then have them model the subtraction on the interactive number lines.

Sample Assessment

In how many ways can you decompose  (5/4) into the sum of two fractions with a denominator of 4? 

Answer: (1/4)+(4/4); (2/4)+(3/4); (0/4)+(5/4).

The Big Idea

Subtracting fractions with like-denominators can be thought of as taking away the number of copies of (a/b) from the number of copies of (c/b). Adding two fractions with like-denominators is the same as joining the first segment (a/b) end to end with the second segment (c/b).

What are the students doing?

Students explore adding and subtracting fractions with the same denominator by using an interactive number line.

What is the teacher doing?

Use the interactive number line to explain why the sum of two fractions has the same denominator as the addends. Guide students in understanding that the denominators of the fractions are not added.