Lesson 10
All Sorts of Denominators
Lesson Purpose
The purpose of this lesson is for students to explain why it is possible to find a common denominator for two given fractions by multiplying the denominators.
Lesson Narrative
In this lesson students begin to develop formal strategies for adding and subtracting fractions. They deal with all cases, including situations where the two denominators share no common factor and cases where the denominators share a large factor. Students show why the product of the two denominators is always a common denominator but are encouraged to use the common denominator that makes sense to them. The discussions focus on different choices students make for a common denominator and how their calculations are the same and different.
- Representation
- MLR8
Learning Goals
Teacher Facing
- Recognize that when adding or subtracting fractions with unlike denominators, a common denominator can be found by multiplying the denominators.
Student Facing
- Let’s find common denominators.
Required Preparation
CCSS Standards
Addressing
Lesson Timeline
| Warm-up | 10 min |
| Activity 1 | 15 min |
| Activity 2 | 20 min |
| Lesson Synthesis | 10 min |
| Cool-down | 5 min |
Teacher Reflection Questions
Reflect on a time your thinking changed about something in class recently. How will you alter your teaching practice to incorporate your new understanding?
Suggested Centers
- How Close? (1–5), Stage 9: Add Fractions to 5 (Addressing)
- Compare (1–5), Stage 6: Add and Subtract Fractions (Supporting)