# Lesson 9

Sumemos números de tres dígitos

## Warm-up: Conversación numérica: Una decena y algunos más (10 minutes)

### Narrative

The purpose of this Number Talk is to elicit strategies and understandings students have for making a ten when adding a one-digit number to three-digit numbers. In the synthesis, the focus is on how students look for ways to make ten. These understandings help students develop fluency and will be helpful in the lesson as students add 2 three-digit numbers and consider composing units.

### Launch

• Display one expression.
• “Hagan una señal cuando tengan una respuesta y puedan explicar cómo la obtuvieron” // “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

### Activity

• Keep expressions and work displayed.
• Repeat with each expression.

### Student Facing

Encuentra mentalmente el valor de cada expresión.

• $$528 + 2$$
• $$528 + 7$$
• $$487 + 3$$
• $$487 + 8$$

### Activity Synthesis

• “¿Qué observan sobre las sumas?” // “What do you notice about the sums?” (I made a ten to find the sum. They all show adding some ones to three-digit numbers. There’s a pattern in the ones—0 ones, 5 ones, 0 ones, 5 ones.)
• “¿Por qué $$528 + 2$$ y $$487 + 3$$ ayudan a encontrar el valor de las otras expresiones?” // “Why are $$528 + 2$$ and $$487 + 3$$ helpful in finding the value of the other expressions?” (We know they make a new ten, so it helped me think about how I could decompose a number to help make a ten.)

## Activity 1: ¿Cómo sumaste números de tres dígitos? (20 minutes)

### Narrative

The purpose of this activity is for students to practice adding within 1,000 with an emphasis on adding by place. Throughout the activity, students have opportunities to explain their methods and representations to peers. In the synthesis, students have opportunities to question and critique the work of their peers as they compare different methods for adding three-digit numbers and different representations that show composing units when adding by place (MP3).

This activity uses MLR8 Discussion Supports. Advances: conversing

Engagement: Provide Access by Recruiting Interest.Provide choice. Invite students to decide which problem to start with and the strategy they feel most comfortable solving with.
Supports accessibility for: Social-Emotional Functioning, Organization, Attention

### Required Materials

Materials to Gather

• Groups of 2

### Activity

• “Vamos a practicar la suma de 2 números de tres dígitos. Pueden encontrar el valor de cada suma de cualquier forma que tenga sentido para ustedes. Después de trabajar individualmente durante un momento, pueden trabajar con un compañero” // “We are going to practice adding 2 three-digit numbers. You can find the value of each sum in any way that makes sense to you. After some time working independently, you can continue working with a partner.”
MLR8 Discussion Supports
• Display sentence frames to support students when they explain their strategy:
• “Primero, yo voy a ______ porque . . .” // “First, I _____ because . . .”
• “Observé ______, entonces yo . . .” // “I noticed _____ so I . . .”
• 5 minutes: independent work time
• 4 minutes: partner work time
• “Escojan una expresión y compartan con otro compañero cómo encontraron el valor de la suma” // “Choose one expression and share how you found the value of the sum with a new partner.”
• 3 minutes: partner discussion
• Monitor for students who use base-ten blocks, base-ten diagrams, or other representations that clearly show adding by place.

### Student Facing

Encuentra el valor de cada expresión. Muestra cómo pensaste.

1. $$384 + 409$$
2. $$757 + 152$$
3. $$262 + 438$$
4. $$575 + 166$$

### Student Response

If students lose track of the tens or hundreds they compose (for example, $$384 + 409 = 783$$) or do not compose a ten or hundred, prompt students to explain their thinking and any representations they use. Consider asking:
• “¿Cómo muestra tu representación que compusiste una unidad en base diez nueva?” // “How does your representation show that you composed a new unit?”
• “¿Qué podrías agregarle a tu representación para mostrar las decenas o centenas que compones?” // “What could you add to your representation to help you keep track of any tens or hundreds you compose?”
• “¿Cómo podrías usar bloques en base diez para mostrar cómo pensaste?” // “How could you use base-ten blocks to show your thinking?”

### Activity Synthesis

• Invite 2–3 previously identified students to share their representations and how they found the value of the sums.
• “¿En qué se parecen estos métodos? ¿En qué son diferentes?” // “How are these methods the same? How are they different?”

## Activity 2: Analicemos y sumemos (15 minutes)

### Narrative

The purpose of this activity is for students to analyze two methods for finding a sum within 1,000. Students use what they know about adding by place and composing units to determine which method shows the correct value of the sum. Students discuss why one method did not work and ways the method could be adjusted to find the correct sum (MP3).

### Required Materials

Materials to Gather

• Groups of 2

### Activity

• “A Noah y a Kiran les pidieron que encontraran el valor de $$267 + 338$$. Tómense un minuto para examinar el trabajo de cada estudiante” // “Noah and Kiran were asked to find the value of $$267 + 338$$. Take a minute to look at each student’s work.”
• 1–2 minutes: quiet think time
• “Discutan en qué se parecen y en qué son diferentes el trabajo de Noah y de Kiran. Después expliquen cuál estudiante encontró el valor correcto de la suma. Muestren cómo lo saben” // “Discuss how Noah and Kiran’s work is the same and how it is different. Then explain which student found the correct value of the sum. Show how you know.”
• 10 minutes: partner work time
• Monitor for groups that match Kiran’s equations to Noah’s diagram to explain where Noah could improve his work.

### Student Facing

Noah y Kiran mostraron cómo encontraron el valor de $$267 + 338$$.

El trabajo de Noah

El trabajo de Kiran

1. ¿En qué se parecen el trabajo de Noah y el de Kiran? ¿En qué son diferentes?

2. ¿Cuál estudiante encontró el valor correcto? Explica o muestra cómo pensaste.

### Activity Synthesis

• “¿En qué se parecen el trabajo de Noah y el de Kiran? ¿En qué son diferentes?” // “How is Noah and Kiran’s work the same? How is it different?” (They both show adding by place. Noah used a base-ten diagram and Kiran used equations. They found different values. Noah forgot to add the ten he made from the ones. He had enough tens to make a hundred.)
• “¿Cuál estudiante encontró el valor correcto de ​​$$267 + 338$$? ¿Cómo lo saben?” // “Which student found the correct value for $$267 + 338$$? How do you know?”
• Invite previously identified students to share.
• “¿En qué parte del trabajo de Kiran ven el paso que le hizo falta a Noah?” // “Where do you see the step Noah missed in Kiran’s work?”

## Lesson Synthesis

### Lesson Synthesis

Display Kiran’s way and any work samples that show different methods from Activity 1.

“Hoy sumamos dos números de tres dígitos y estudiamos diferentes métodos y representaciones” // “Today we added two three-digit numbers and looked at different methods and representations.”

“¿En qué se parecen los métodos y representaciones que vieron hoy? ¿En qué son diferentes?” // “How are the methods and representations you saw today the same? How are they different?”

“¿Cuál método prefieren? ¿Cuál les gustaría practicar más?” // “Which method do you prefer? Which would you like to practice more?”