Lesson 8
Addition of Fractions
Warmup: Notice and Wonder: A Fraction on a Number Line (10 minutes)
Narrative
Launch
 Groups of 2
 Display the number line diagram.
 “What do you notice? What do you wonder?”
 1 minute: quiet think time
Activity
 “Discuss your thinking with your partner.”
 1 minute: partner discussion
 Share and record responses.
Student Facing
What do you notice? What do you wonder?
Student Response
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Activity Synthesis
 “What does the space between any two tick marks represent?” (A third) “How do you know?” (If five spaces represent 5 thirds and the spaces are the same size, then each space is 1 third.)
 “Where is 1 on the number line?” (The third tick mark from 0) “Where is 2?” (The sixth tick mark from 0, or 1 tick mark to the right of \(\frac{5}{3}\))
 “Today we’ll use number lines to help us reason about sums of fractions.”
Activity 1: Sum of Jumps (20 minutes)
Narrative
This activity prompts students to use number lines to illustrate the decomposition of a fraction into sums of other fractions, reinforcing their work from an earlier lesson. Along the way, students recognize that one way to decompose a fraction greater than 1 is to write it as a sum of a whole number and a fraction less than 1. This insight prepares students to interpret and write mixed numbers in later activities.
Supports accessibility for: Conceptual Processing, VisualSpatial Processing, Organization
Launch
 Display or draw this number line:
 “What number does the point describe?” (8)
 “What do you think the ‘jumps’ represent?” (The numbers that are put together to go from 0 to 8)
 “What equations can we write to represent the combination of jumps?” (\(6 + 2 =8\) or \(2 + 6 = 8\))
 “Let’s look at the jumps on some other number lines and see what they may represent.”
Activity
 Groups of 2
 “Work independently on the activity for a few minutes. Afterwards, share your responses with your partner.”
 5–7 minutes: independent work time
 2 minutes: partner discussion
Student Facing

 On each number line, draw two “jumps” to show how to use sixths to make a sum of \(\frac{8}{6}\). Then, write an equation to represent each combination of jumps.
 Noah draws the following diagram and writes: \(\frac{8}{6} = \frac{6}{6} + \frac{2}{6}\) and \(\frac{8}{6} = 1 + \frac{2}{6}\). Which equation is correct? Explain your reasoning.

 On each number line, draw “jumps” to show how to use thirds to make a sum of \(\frac{7}{3}\). Then, write an equation to represent each combination of jumps.
 Write \(\frac{7}{3}\) as a sum of a whole number and a fraction.
Student Response
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Advancing Student Thinking
Activity Synthesis
 Invite students to share their equations. Record them for all to see.
 Focus the discussion on part b: writing \(\frac{7}{3}\) as a sum of a whole number and a fraction. Students are likely to write \(1 + \frac{4}{3}\) and \(2 + \frac{1}{3}\).
 Explain that \(2 + \frac{1}{3}\) can be written as \(2\frac{1}{3}\), which we call a mixed number. This number is equivalent to \(\frac{7}{3}\).
 “Why might it be called a mixed number?” (It is a mix of a whole number and a fraction.)
Activity 2: What is the Sum? (15 minutes)
Narrative
In this activity, students use number lines to represent addition of two fractions and to find the value of the sum. The addends include fractions greater than 1, which can be expressed as a sum of a whole number and a fraction. Students practice constructing a logical argument and critiquing the reasoning of others when they explain which of the strategies they agree with and why (MP3).
Advances: Speaking, Conversing
Launch
 Groups of 2
 Draw students’ attention to the four addition expressions in the first problem.
 “What do you notice about the numbers? Make some observations.” (Sample responses:
 They all have 8 for the denominator but different numbers for the numerator.
 Some fractions are less than 1 and others are greater than 1.
 There is one mixed number.)
 “What do you notice about the number lines?” (They are identical. They are all partitioned into eighths.)
Activity
 “Take 5–7 minutes to work on the task independently. Then, discuss your responses with your partner.”
 5–7 minutes: independent work time
 2–3 minutes: partner discussion
 Monitor for students who can explain why Priya, Kiran, and Tyler might each be correct.
Student Facing

Use a number line to represent each addition expression and to find its value.
 \(\frac{5}{8} + \frac{2}{8}\)
 \(\frac{1}{8} + \frac{9}{8}\)
 \(\frac{11}{8} + \frac{9}{8}\)
 \(2\frac{1}{8} + \frac{4}{8}\)
 Priya says the sum of \(1\frac{2}{5}\) and \(\frac{4}{5}\) is \(1\frac{6}{5}\). Kiran says the sum is \(\frac{11}{5}\). Tyler says it is \(2\frac{1}{5}\). Do you agree with any of them? Explain or show your reasoning. Use one or more number lines if you find them helpful.
Student Response
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Advancing Student Thinking
Activity Synthesis
 Invite students to share their responses to the first problem.
 “Look at the sums you found. What do you notice about the numbers in each sum? How do they relate to the numbers in the fractions being added?” (The denominator of the sum is 8. The numerator of the sum is the result of adding the numerators of the addends.)
 Select previously identified students to share their responses to the second problem.
 If no students use number lines to make their case, consider sketching or displaying these diagrams.
 Point out that although it is true that \(\frac{11}{5} = 1 + \frac{6}{5}\), we don’t usually write \(1\frac{6}{5}\) as the mixed number equivalent to \(\frac{11}{5}\). Because we can make another 1 whole with \(\frac{6}{5}\), or \(1+1+\frac{1}{5}\) , we'd instead write \(2\frac{1}{5}\).
Activity 3: Make Two Jumps [OPTIONAL] (20 minutes)
Narrative
This optional activity gives students an additional opportunity to practice using number lines to decompose fractions into sums of other fractions and to record the decompositions as equations.
The fractions on the cards (shown here) contain no whole numbers or mixed numbers, but some students may use them to help them find the second addend (and to avoid counting tick marks on the number line). Some may also choose to label each number line with whole numbers beyond 1 to facilitate their reasoning and equation writing.
\(\frac{1}{3} \qquad \frac{2}{3} \qquad \frac{3}{3} \qquad \frac{4}{3} \qquad \frac{5}{3} \qquad \frac{6}{3} \qquad \frac{7}{3} \qquad \frac{8}{3}\)
Required Materials
Materials to Copy
 Make Two Jumps
Required Preparation
 Create a set of cards from the blackline master for each group of 2.
Launch
 Groups of 2
 Give each group a set of fraction cards from the blackline master.
 Display the four number lines.
 “What do you notice? What do you wonder?”
 30 seconds: quiet think time
 30 seconds: partner discussion
Activity
 “Label each point on the number line with a fraction it represents.”
 1–2 minutes: independent work time
 “You will make two jumps on the number line to go from 0 to the point and write an equation to represent your moves.”
 Explain how to use the cards and how to complete the task. Consider demonstrating with an example and allowing students to ask clarifying questions before they begin.
 Monitor for students who:
 use whole numbers and mixed numbers in their equations and those who don’t
 label their number lines with whole numbers beyond 1
Student Facing
Here are four number lines, each with a point on it.
For each number line, label the point. This is your target. Make two forward jumps to get from 0 to the target.
 Pick a card from the set given to you. Use the fraction on it for your first jump. Draw the jump and label it with the fraction.
 From there, draw the second jump to reach the target. What fraction do you need to add? Label the jump with the fraction.
 Write an equation to represent the sum of your two fractions.
Student Response
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Activity Synthesis
 Select previously identified students to share their responses to the first couple of diagrams (or more if time permits). Start with students who used no whole numbers or mixed numbers. Ask them to explain why they chose to write the numbers the way they did.
 Consider discussing the merits and challenges (if any) of expressing the fractions as whole or mixed numbers.
Lesson Synthesis
Lesson Synthesis
“Today, we used number lines to decompose fractions into sums of smaller fractions, or sums of a whole number and a fraction. We also learned that a fraction greater than 1 can be written as a mixed number.”
“How would you explain to a classmate who is absent today what a mixed number is?” (It's a number written as a whole number and a fraction.)
“Let’s look at some sums you found in the second activity. Which ones can be written as mixed numbers and why?” (\(\frac{10}{8}\) and \(\frac{20}{8}\), because they are greater than 1.)
“What mixed number is equivalent to each of those fractions? How do you know?” (\(1\frac{2}{8}\) and \(2\frac{4}{8}\):
 \(1\frac{2}{8}\) is equivalent to \(\frac{10}{8}\) because \(\frac{10}{8} = \frac{8}{8} + \frac{2}{8}\) and \(\frac{8}{8}\) is 1.
 \(2\frac{4}{8}\) is equivalent to \(\frac{20}{8}\) because \(\frac{16}{8}\) is 2 wholes and adding \(\frac{4}{8}\) more gives \(\frac{20}{8}\).)
Cooldown: Lucky Thirteentenths (5 minutes)
CoolDown
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