# Lesson 2

Formemos centenas

## Warm-up: Conteo grupal: Contemos de 10 en 10 (10 minutes)

### Narrative

The purpose of this Choral Count is for students to practice counting by 10 beyond 120 and notice patterns in the count. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to recognize multiples of 100 written as numerals and make connections between groups of 10 tens and hundreds.

### Launch

• “Contemos de 10 en 10, empezando en 0” // “Count by 10, starting at 0.”
• Record as students count. Record 10 numbers in each row. Then start a new row directly below.
• Stop counting and recording at 300.

### Activity

• “¿Qué patrones ven?” // “What patterns do you see?”
• 12 minutes: quiet think time
• Record responses.

### Activity Synthesis

• “¿Quién puede describir el patrón con otras palabras?” // “Who can restate the pattern in different words?”

## Activity 1: Formemos centenas (20 minutes)

### Narrative

The purpose of this activity is for students to use groups of 10 tens to compose multiples of 100. Students use base-ten blocks to make a group of 10 tens and exchange it for 1 hundred. They find the total number of tens and represent the same quantity with hundreds. When students make connections between the number of tens and hundreds they need to represent each number and the digits in the three-digit number, they look for and express regularity in repeated reasoning (MP8).

If you do not have enough base-ten blocks for groups of 4, you can make larger groups of students to use fewer blocks.

MLR8 Discussion Supports. Synthesis: At the appropriate time, give students 2–3 minutes to make sure that everyone in their group can explain what they notice about the number of tens and the number of hundreds in each problem. Invite groups to rehearse what they will say when they share with the whole class.

### Required Materials

Materials to Gather

### Required Preparation

• Each group of 4 students will need at least 50 ten blocks. Do not include hundreds blocks for this activity.

### Launch

• Groups of 4
• Give each group at least 50 base-ten blocks.
• “Ayer vimos distintas formas de representar el 100 con decenas, con unidades y también como 1 unidad llamada ‘una centena’” // “Yesterday, we looked at different ways to represent 100 with tens, ones, and as 1 unit called a hundred.”

### Activity

• “Hoy vamos a usar bloques en base diez para representar números que son mayores que 100” // “Today, we are going to use base-ten blocks to represent numbers that are larger than 100.”
• “Con su grupo, usen sus bloques en base diez para representar los números que se muestran” // “Work with your group to represent the numbers shown with your base-ten blocks.”
• 10 minutes: small-group work time
• Monitor for groups that discuss ways to represent 300 by:
• using base-ten blocks and organizing into groups of 10 tens
• reasoning that if 1 hundred is 10 tens, then 2 hundreds is 20 tens, and 3 hundreds is 30 tens
• connecting patterns in the number of tens to the numerals and digits.

### Student Facing

1. Forma cada número usando bloques en base diez. Anota cuántos bloques de decena usas.

1. Forma el 90.

2. Forma el 110.

3. Forma el 150.

____________ decenas

____________ decenas

____________ decenas

2. ¿Cuántos bloques en base diez necesitarías para formar el 200?

____________ decenas

3. ¿Cuántos bloques en base diez necesitarías para formar el 300?

____________ decenas

4. ¿Cuántos bloques en base diez necesitarías para formar el 300 si pudieras usar 1 bloque de centena?

1 centena ____________ decenas

5. ¿Cuántas decenas necesitarías para formar el 300 si pudieras usar 2 bloques de centena?

2 centenas ____________ decenas

6. ¿Cuántas decenas necesitarías para formar el 300 si pudieras usar solo bloques de centena?

____________ centenas ____________ decenas

### Activity Synthesis

• Invite previously identified students to share how they reasoned about ways to represent 300.
• “¿Qué observaron sobre el número de decenas y el número de centenas?” // “What did you notice about the number of tens and the number of hundreds?” (10 tens = 1 hundred, 20 tens = 2 hundreds, 30 tens = 3 hundreds)
• “¿Cuántas centenas tendría si tuviera 80 decenas?” // “How many hundreds would I have if I have 80 tens?” (8 hundreds)

## Activity 2: ¿Cuántas centenas? (15 minutes)

### Narrative

The purpose of this activity is for students to make sense of representations of more than 1 hundred. Students recognize that base-ten diagrams can be used to represent hundreds even when all of the ones are not outlined. Students make connections between multiples of 10 and multiples of 100, as they consider the relationship between 70 tens and 7 hundreds. Students describe how grouping tens and counting units of 1 hundred help to count and represent large numbers.

Action and Expression: Internalize Executive Functions. Synthesis: Check for understanding by inviting students to rephrase how ones, tens, and hundreds can all be used to represent the number 700 in their own words. Keep a display of their responses to reiterate this content.
Supports accessibility for: Memory, Organization

### Required Materials

Materials to Gather

• Groups of 24

### Activity

• “Han y Jada representaron 700 usando bloques en base diez, números y palabras” // “Han and Jada represented 700 using base-ten blocks, numbers, and words.”
• “Ambos iban a dibujar diagramas en base diez, pero se quedaron sin tiempo” // “They were both going to draw a base-ten diagram, but ran out of time.”
• “En su grupo, usen bloques en base diez para representar el trabajo de cada estudiante” // “Represent each student’s work with base-ten blocks in your group.”
• “Luego, discutan cada pregunta juntos” // “Then, discuss each question together.”
• 10 minutes: group work time
• Monitor for groups that organize their tens into groups of ten and count each group as 1 hundred.

### Student Facing

Han y Jada representaron el mismo número usando bloques en base diez. Ellos empezaron con diagramas en base diez, pero se quedaron sin tiempo para terminarlos.

Han

Solo usé centenas.

Solo usé decenas.

Valor total: 700

Valor total: 700

1. Usa bloques en base diez. Muestra cómo se vería el trabajo de cada estudiante si hubieran tenido tiempo para terminarlo.

2. Explica cómo sabes que ambas maneras de usar bloques en base diez muestran 700.
3. Completa el diagrama en base diez de Jada.
4. Explica por qué crees que Han se quedó sin tiempo para terminar su diagrama.

### Student Response

If students count out 70 tens to show Han’s work, but do not organize the tens into groups, consider asking:

• “¿Cuál es el valor de todas estas decenas? ¿Cómo puedes mostrarlo?” // “What is the value of all these tens? How can you prove that?”
• “¿Cómo puedes organizar las decenas para que sea más fácil ver el valor total?” // “How could you organize the tens so it’s easier to see the total value?”

### Activity Synthesis

• “¿Cómo saben que se muestra 700 de la manera que Jada lo quería hacer?” // “How do you know that Jada’s way shows 700?” (You could count each hundred block by 1. You could count the squares by 1. If there are 7 hundred blocks, then it shows 700.)
• Invite previously selected identified groups to share how they organized their blocks when using Han’s way.

## Lesson Synthesis

### Lesson Synthesis

“Hoy usamos bloques y diagramas en base diez para representar números que son mucho mayores que 100” // “Today we used base-ten blocks and diagrams to represent numbers that are much greater than 100.”

“¿Cuál forma de representar 700 piensan que fue más fácil: la de Jada o la de Han? Expliquen” // “Which way do you think was easier to represent 700, Jada’s way or Han’s way? Explain.” (Jada’s way. It’s faster to just count out 7 blocks than 70 blocks. It was easier to make sure we were showing 700.)

“En la forma de Han se usaron 70 bloques en total. ¿Cómo podrían representar 700 usando la mayor cantidad posible de bloques?” // “Han’s way used 70 total blocks. How could you represent 700 with the greatest amount of blocks?” (You could use 700 ones.)