# Lesson 19

Formemos números de dos dígitos

## Warm-up: Cuál es diferente: Distintas maneras de mostrar un número (10 minutes)

### Narrative

This warm-up prompts students to compare four different base-ten representations. It gives students a reason to use language precisely. It gives the teacher an opportunity to hear how students use terminology and talk about characteristics of the items in comparison to one another. During the synthesis, ask students to explain the meaning of any terminology they use, especially as it relates to tens, ones, and the value of digits.

### Launch

• Groups of 2
• Display the image.
• “Escojan una que sea diferente. Prepárense para compartir por qué es diferente” // “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

### Activity

• “Discutan con su pareja lo que pensaron” // “Discuss your thinking with your partner.”
• 2–3 minutes: partner discussion
• Share and record responses.

### Student Facing

¿Cuál es diferente?

### Activity Synthesis

• “Encontremos al menos una razón por la que cada una es diferente” // “Let’s find at least one reason why each one doesn’t belong.”

## Activity 1: Usemos decenas y unidades para formar 65 (15 minutes)

### Narrative

The purpose of this activity is for students to create a collection of 65 using only 5 towers of 10 and single cubes. Students are told that they cannot physically create any new towers or take apart any towers. As students work, they recognize that there are only 5 tens and consider how many ones are needed to get to 65. Some students may count on from 50 to 65 and other students may apply what they have learned in previous lessons to determine they need 1 more ten and 5 more ones, or 15 (MP2). As students represent their collection, they may show the number of towers of 10 they used and how many ones, including 5 tens and 15 ones, or that they grouped 10 of the ones in some way. This includes clearly marking a group of 10 ones.

Students may label their drawings using numbers, a combination of numbers and words, or expressions (MP6).

### Required Materials

Materials to Gather

### Required Preparation

• Each group of 3-4 needs a bag of connecting cubes in 5 towers of 10 and 4 or 5 handfuls of singles.

### Launch

• Groups of 3–4
• Give each group one bag of connecting cubes.

### Activity

• 10 minutes: partner work time
• As students work, consider asking:
• “¿Cómo organizaron su conteo?” // “How did you organize your count?”
• “¿Cómo van a mostrar de qué manera organizaron y contaron?” // “How will you show how you organized and counted?”
• Monitor for students who represent the count as 5 tens and 15 ones in different ways.

### Student Facing

Haz una colección de 65.
No puedes separar ninguna de las torres.
No puedes hacer ninguna torre nueva.

Muestra tu colección de una manera que los demás entiendan.

Si te queda tiempo, piensa en otra manera de formar 65 usando los cubos de la bolsa.

### Student Response

If students start counting the ones and are not sure what to do when they do not have enough, consider asking:

• “Cuéntame más acerca de cómo planeas formar 65” // “Tell me more about how you are planning to make 65.”
• “¿Cómo podemos usar las torres de 10 para formar 65?” // “How can we use the towers of 10 to help us make 65?”

### Activity Synthesis

• Invite previously identified students to share.
• “¿De qué manera cada una de estas representaciones muestra 65? ¿En qué se parecen estas representaciones? ¿En qué son diferentes?” // “How do each of these representations show 65? How are these representations the same? How are they different?” (They all show some tens and some ones. One shows 15 ones and the other shows 10 ones in a group and then 5 more ones. One shows an expression and the others don't.)

## Activity 2: Formemos 37 de diferentes maneras (10 minutes)

### Narrative

The purpose of this activity is for students to represent 37 with tens and ones in different ways. It is not necessary that students find all the ways to represent 37, rather that they see that the number can be represented with different amounts of tens and ones. Students are given connecting cubes in towers of 10 and singles, and they represent their thinking on paper using drawings, numbers, or words. Some students may initially represent 37 using 3 tens and 7 ones and then notice that they can decompose a tower of 10 into 10 singles and have 2 tens and 17 ones and use this structure to find other ways. Students may represent 37 as $$36 + 1$$, $$35 + 2$$, etc., which are all valid ways to represent the number. The lesson synthesis focuses on representing 37 with different groups of tens and ones.

MLR7 Compare and Connect. Synthesis: After all methods have been presented, lead a discussion comparing, contrasting, and connecting the different approaches. Ask, “¿En qué se parecen las representaciones? ¿En qué son diferentes? ¿De qué manera cada una muestra las decenas y las unidades?” // “How are representations the same? How are they different? How do they each show tens and ones?”
Action and Expression: Internalize Executive Functions. Invite students to plan a method with their partners, including the tools they will use, for decomposing 37 in multiple ways.
Supports accessibility for: Organization, Attention

### Launch

• Groups of 2
• Give each group connecting cubes in towers of 10 and singles.
• “Acabamos de ver que podemos formar 65 sin usar seis decenas. Ahora van a encontrar diferentes maneras de formar el número 37. Encuentren todas las maneras que puedan usando los cubos encajables. Después, muestren cada una de las diferentes maneras con dibujos, números o palabras” // “We just saw that we can make 65 without using six tens. Now you are going to find different ways to make the number 37. Find as many different ways as you can with the connecting cubes. Then show each different way with drawings, numbers, or words.”

### Activity

• 2 minutes: quiet think time
• 5–6 minutes: partner work time
• Monitor for students who strategically find different ways to compose 37 using towers of 10 and singles including:
• Start with 3 tens and 7 ones, and decompose each tower of 10 into singles.

### Student Facing

¿De cuántas maneras puedes formar 37?
Muestra cómo pensaste. Usa dibujos, números o palabras.

### Activity Synthesis

• Invite previously identified students to share.
• Record each way students made 37.
• “¿Qué observan sobre las maneras en las que ellos formaron 37?” // “What do you notice about the ways they made 37?” (They both made 37 in the same ways. One student started with all ones and made one ten at a time. The other student started with 3 tens and broke one ten apart at a time. Each time a ten was made, there were 10 fewer ones. Each time a 10 was broken apart, there were 10 more ones.)

## Activity 3: Centros: Momento de escoger (15 minutes)

### Narrative

The purpose of this activity is for students to choose from activities that offer practice working with two-digit numbers.

• Greatest of Them All
• Get Your Numbers in Order
• Grab and Count

### Required Materials

Materials to Gather

### Required Preparation

• Gather materials from previous centers:
• Greatest of Them All, Stage 1
• Get Your Numbers in Order, Stage 1
• Grab and Count, Stage 2

### Launch

• Groups of 2
• “Ahora van a a escoger un centro de los que ya conocemos” // “Now you are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Piensen qué les gustaría hacer” // “Think about what you would like to do.”
• 30 seconds: quiet think time

### Activity

• Invite students to work at the center of their choice.
• 10 minutes: center work time

### Student Facing

Escoge un centro.

El más grande de todos

Ordena tus números

Agarra y cuenta

### Activity Synthesis

• “¿Cómo trabajaron hoy con números de dos dígitos durante el tiempo de centros?” // “How did you work with two-digit numbers during center time?”

## Lesson Synthesis

### Lesson Synthesis

“Hoy formamos números de dos dígitos de diferentes maneras. Usamos distintas cantidades de decenas y unidades para formar el mismo número” // “Today we made two-digit numbers in different ways. We used different amounts of tens and ones to make the same number.”

• Display 3 tens and 7 ones, 2 tens and 17 ones, 1 ten and 27 ones, 37 ones.
• “¿Cuál piensan que corresponde mejor al número de dos dígitos 37? ¿Por qué piensan que corresponde mejor al número?” // “Which do you think best matches the two-digit number 37? Why do you think it matches the number best?” (3 tens and 7 ones matches best because the digits in the number tell us that there are 3 tens and 7 ones. 37 ones matches best because the number is read ‘thirty-seven.’)