# Lesson 16

Sumemos tres números

### Lesson Purpose

The purpose of this lesson is for students to apply the commutative and associative properties in order to make a ten when adding three numbers within 20, and make sense of equations with addition expressions on both sides of the equal sign.

### Lesson Narrative

In the previous lesson students found the sum of three addends in which two addends made a ten. They considered different methods for finding the sums. In this lesson, students make sense of equations with addition expressions on both sides of the equal sign. One of the expressions has three addends, two of which make 10. Students apply what they learned about the commutative and associative properties to match these expressions to a \(10 + n\) expression, and determine whether equations are true or false.

- Representation

- MLR2

### Learning Goals

Teacher Facing

- Make sense of equations with addition expressions on both sides of the equal sign (For example, \(3 + 6 + 7 = 10 + 6\)).
- Use the associative property to make a ten when adding three numbers.

### Student Facing

- Sumemos 3 números.

### Required Materials

Materials to Gather

### Required Preparation

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 15 min |

Activity 2 | 10 min |

Activity 3 | 10 min |

Lesson Synthesis | 10 min |

Cool-down | 5 min |

### Teacher Reflection Questions

Think about a time you recently made a mistake during math class. How did you leverage your mistake to show students that mistakes are just learning in process?