# Lesson 20

Will it Always Work? (optional)

### Lesson Purpose

The purpose of this lesson is for students to explain how the product of two numbers compares to one factor based on the size of the other factor.

### Lesson Narrative

The goal of this optional lesson is to compare the size of a product to the size of one factor, applying what students have learned in the last several lessons. They make the comparisons and describe in general how to make comparisons using a strategy that makes sense to them. No representation is provided or suggested so this gives students an opportunity to think about the different methods they have learned, namely calculation, number lines and the distributive property, and choose the one that makes sense in each situation.
• Representation
• MLR1

### Learning Goals

Teacher Facing

• Make generalizations about multiplying a whole number by a fraction greater than, less than, or equal to 1.

### Student Facing

• Let’s make generalizations about multiplying a whole number by a fraction.

### Lesson Timeline

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

### Teacher Reflection Questions

What questions did you ask today that helped students reason about the size of a product without performing multiplication?

### Suggested Centers

• Rectangle Rumble (3–5), Stage 5: Fraction Factors (Addressing)
• Rolling for Fractions (3–5), Stage 4: Multiply Fractions (Supporting)

### Print Formatted Materials

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