# Lesson 9

Use Equivalent Expressions

### Lesson Purpose

The purpose of this lesson is for students to add and subtract fractions with unlike denominators by replacing the given expressions with equivalent expressions with common denominators.

### Lesson Narrative

In a previous lesson, students saw that having a common denominator is useful for adding or subtracting fractions. In this lesson students add and subtract fractions using equivalent expressions where the fractions have the same denominator. Students work with denominators where one is a multiple of the other so they only need to change the denominator in one of the 2 fractions. In each case the numerators are chosen so that either denominator works as a common denominator and students compare different strategies for finding the sum or difference.

- Action and Expression

- MLR8

### Learning Goals

Teacher Facing

- Use equivalent expressions to add and subtract fractions with unlike denominators.

### Student Facing

- Let’s use equivalent expressions to add and subtract fractions with unlike denominators.

### Required Preparation

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 15 min |

Activity 2 | 15 min |

Activity 3 | 10 min |

Lesson Synthesis | 10 min |

Cool-down | 5 min |

### Teacher Reflection Questions

How effective were your questions in advancing students’ thinking today? What did students say or do that showed they were effective?

### Suggested Centers

- Would You Rather? (2–5), Stage 3: Compare Units in a Given System (Addressing)
- Compare (1–5), Stage 6: Add and Subtract Fractions (Supporting)