# Lesson 19

Métodos para sumar hasta 20

### Lesson Purpose

The purpose of this lesson is for students to analyze addition methods for adding within 20, then use those methods flexibly to find sums based on the numbers in a given expression.

### Lesson Narrative

In previous lessons, students decomposed an addend in order to make a ten and thought about sums as equivalent \(10 + n\) expressions. They applied the commutative and associative properties to find the sum more easily. Students looked for and used patterns in addition expressions (such as \(4 + 8 = 5 + 7\)). In this lesson, students continue adding within 20.

Students may use any method they choose, but are encouraged to think about methods which may work better for certain sums. In the first activity, students analyze three different methods for finding a sum, all of which include decomposing an addend to make a known sum. In the second activity, students find sums within 20 and share their thinking with a partner.

- Action and Expression

- MLR8

### Learning Goals

Teacher Facing

- Analyze methods for adding within 20.
- Use addition methods flexibly to find sums based on the numbers in a given problem.

### Student Facing

- Sumemos hasta 20.

### Required Materials

Materials to Gather

### Required Preparation

Activity 2:

- Each group needs a set of the Compare Stage 2 Addition Cards cards from the previous lesson.

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 20 min |

Activity 2 | 20 min |

Lesson Synthesis | 10 min |

Cool-down | 0 min |

### Teacher Reflection Questions

What methods are students using to find sums? Which methods were you expecting and which surprised you?