Lesson 13
Put It All Together: Add and Subtract Fractions
Lesson Purpose
Lesson Narrative
In this lesson, students examine and implement different strategies to find a common denominator when adding or subtracting fractions. For any pair of fractions, the product of the denominators will be a common denominator and in many cases this is also the smallest choice of common denominator. In other cases, however, there is a smaller choice than the product and sometimes this can be a useful choice. For example, the sum \(\frac{3}{20} + \frac{9}{50}\) can be found using 1,000 as a common denominator but it can also be found with 100 as a common denominator. Either choice will work and there are reasons for preferring each strategy. In this lesson, students think about these ideas as they investigate different common denominators for finding sums and differences of fractions.
 Engagement
 MLR8
Learning Goals
Teacher Facing
 Add and subtract fractions with unlike denominators.
Student Facing
 Let’s add and subtract fractions with unlike denominators.
Required Preparation
CCSS Standards
Addressing
Lesson Timeline
Warmup  10 min 
Activity 1  20 min 
Activity 2  15 min 
Lesson Synthesis  10 min 
Cooldown  5 min 
Teacher Reflection Questions
Suggested Centers
 How Close? (1–5), Stage 9: Add Fractions to 5 (Addressing)
Print Formatted Materials
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Additional Resources
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