Lesson 8

Addition of Fractions

Lesson Purpose

The purpose of this lesson is for students to use a number line to reason about addition of fractions with the same denominator, and to decompose fractions greater than 1 into a whole number and a fraction less than 1.

Lesson Narrative

Previously, students decomposed non-unit fractions into smaller unit and non-unit fractions. Here they continue to think about decomposing fractions, but they now use number line diagrams to support their reasoning.

A number line can illustrate the number of unit fractions that make a whole number. This in turn allows students to see that a fraction greater than 1 can be decomposed into a whole number and a fraction less than 1, preparing them to work with mixed numbers. For instance, on a number line partitioned into fifths, the fraction \(\frac{7}{5}\) is 7 fifths away from 0 and 2 fifths away from 1, so we can express \(\frac{7}{5}\) as 1 and \(\frac{2}{5}\). One way to illustrate that sum is by drawing “jumps” on the number line.

Number line.

Note that in grade 3, students came across mixed numbers in the context of measurement. For instance, they use inch rulers to measure lengths greater than 1 inch to the nearest halves and fourths, express them using numbers such as \(2\frac{1}{4}\) and \(5\frac{1}{2}\). They did not, however, reason about mixed numbers as sums of smaller fractions or sums of a fraction and a whole number. 

  • Action and Expression
  • MLR8

Learning Goals

Teacher Facing

  • Decompose fractions greater than 1 into a sum of a whole number and a fraction less than 1.
  • Reason about addition of fractions with the same denominator using a number line.

Student Facing

  • Let’s explore sums of fractions on a number line.

Required Materials

Materials to Copy

  • Make Two Jumps

Required Preparation

Activity 3:

  • Create a set of cards from the blackline master for each group of 2.

CCSS Standards


Building Towards

Lesson Timeline

Warm-up 10 min
Activity 1 20 min
Activity 2 15 min
Activity 3 20 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

Students have previously represented whole numbers and fractions on the number line. How did you leverage that experience to help them reason about addition of fractions on the number line?

Suggested Centers

  • Rolling for Fractions (3–5), Stage 2: Multiply a Fraction by a Whole Number (Addressing)
  • Estimate and Measure (1–4), Stage 3: Quarter Inches (Supporting)
  • Target Measurements (2–5), Stage 2: Quarter Inches (Supporting)

Print Formatted Materials

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Student Task Statements pdf docx
Lesson Cover Page pdf docx
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Teacher Presentation Materials pdf docx
Blackline Masters zip

Additional Resources

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