# Lesson 17

Formemos 10 para sumar

### Lesson Purpose

### Lesson Narrative

In previous lessons, students recognized the \(10 + n\) structure of teen numbers and used the structure to find the sum of three numbers. In this lesson, students use the structure of the 10-frame to find the sum of two addends when one addend is 9. Students come to see that when they find the sum of two addends, they can decompose one addend to make 10 with the other addend (associative property). For example, \(9 + 5 = 9 + 1 + 4 = 10 + 4 = 14\). When students identify and use equivalent expressions, they look for and make use of structure (MP7) and here they repeatedly make a 10 to find the value of expressions (MP8).

Student methods are recorded with equations. It may also be helpful to represent how one addend is decomposed in order to make a ten.

- Engagement

- MLR7

Activity 2: Las aves de Clare

### Learning Goals

Teacher Facing

- Analyze methods for adding within 20 that involve making a ten.
- Look for and use patterns in addition expressions to add within 20.

### Student Facing

- Busquemos patrones y pensemos en formar 10 mientras sumamos.

### Required Materials

Materials to Gather

### Required Preparation

Activity 1:

- Each group of 2 needs a set of Number Cards (0-10).

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 20 min |

Activity 2 | 15 min |

Lesson Synthesis | 10 min |

Cool-down | 5 min |