# Lesson 3

Prime and Composite Numbers

### Lesson Purpose

The purpose of this lesson is for students to identify factor pairs and determine whether a given whole number in the range 1–100 is prime or composite.

### Lesson Narrative

In previous lessons, students were introduced to the terms “multiples” and “factor pairs.” In this lesson, they learn that whole numbers can be classified as prime or composite based on the number of factor pairs they have.

Students reason about these numbers in terms of the area and pairs of side lengths of rectangles. They learn that a prime number has exactly 1 factor pair—1 and the number itself, and that a composite number has more than 1 factor pair. They relate “prime” to a number that could represent the area of only one rectangle (with only one pair of side length) and “composite” to a number that could represent the area of multiple rectangles (with multiple pairs of side lengths).

Math Community

Tell students that, at the end of the lesson, they will be asked to identify specific actions they personally experienced from their “Doing Math” list (both teacher and student sections).

• Engagement
• MLR8

### Learning Goals

Teacher Facing

• Determine whether a given whole number in the range 1–100 is prime or composite.
• Find the factor pairs of a given whole number 1–100.

### Student Facing

• Let’s identify prime and composite numbers.

### Required Materials

Materials to Gather

Materials to Copy

• Card Sort: Area

### Required Preparation

Activity 1:

• Create a set of cards from the blackline master for each group of 2.

### 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

Which voices went unheard in math class today? How might you leverage each student's ideas and support them being heard and seen in tomorrow's lesson?

### Suggested Centers

• Find the Number (4), Stage 1: Factors (Addressing)
• Five in a Row: Multiplication (3–5), Stage 1: Factors 1–5 and 10 (Supporting)