# Lesson 3

Contemos para sumar y restar

## Warm-up: Conteo grupal: Hacia adelante y hacia atrás (10 minutes)

### Narrative

The purpose of this warm-up is for students to count backward from 10 and 20. By counting backward from 10 to 1 and 20 to 1, students develop fluency with the count sequence to 20, which will be helpful later in this lesson when students use their knowledge of the count sequence to determine one more and one less than a given number. As students count backward, point to the numbers posted so that students can follow along.

### Launch

• “Contemos hasta 20” // “Let’s count to 20.”
• Record as students count.
• “Esta vez, en lugar de empezar en 1 y contar hacia adelante, vamos a empezar en 10 y a contar hacia atrás hasta que lleguemos a 1. Empecemos en 10 y contemos hacia atrás hasta 1” // “This time, instead of starting a 1 and counting forward, we are going to start at 10 and count backward until we get to 1. Let’s start at 10 and count backward to 1.”

### Activity

• Repeat 3–4 times.
• “Empecemos en 20 y contemos hacia atrás hasta 1” // “Let’s start at 20 and count backward to 1.”
• Repeat 2–3 times.

### Activity Synthesis

• “En la lección de hoy, vamos a resolver problemas-historia en los que contar hacia adelante o hacia atrás les puede ayudar” // “In today’s lesson we will solve story problems where counting forward and backward may help you.”

## Activity 1: Viajar en bus (10 minutes)

### Narrative

The purpose of this activity is for students to use their knowledge of the count sequence to solve Add To, Result Unknown and Take From, Result Unknown story problems where one is added or taken away.

MLR8 Discussion Supports. Before beginning group work time, invite a small number of students to act out the story. Listen for and clarify any questions.

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students access to connecting cubes and 10-frames.
• “Hoy van a resolver dos problemas-historia sobre personas que viajan en un bus” // “Today you are going to solve two story problems about people on a bus.”

### Activity

• Read the first story problem.
• “Cuéntenle a su pareja lo que sucedió en la historia” // “Tell your partner what happened in the story.”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Monitor for students who accurately retell the story. Choose at least one student to share with the class.
• “Muestren cómo pensaron. Usen dibujos, números, palabras u objetos” // “Show your thinking using drawings, numbers, words, or objects.”
• 2 minutes: quiet work time
• 2 minutes: partner discussion
• Repeat the steps with the second story problem.
• Monitor for a student who can explain how they just knew the answer without making a representation.

### Student Facing

1. Había 7 personas en el bus.
Después, 1 persona más subió al bus.
¿Cuántas personas hay ahora en el bus?

Muestra cómo pensaste. Usa objetos, dibujos, números o palabras.

_______________

2. Había 10 personas en el bus.
Después, 1 persona bajó del bus.
¿Cuántas personas hay ahora en el bus?

Muestra cómo pensaste. Usa objetos, dibujos, números o palabras.

_______________

### Activity Synthesis

• Invite a previously identified student to share how they solved the second story problem.

## Activity 2: Estudiantes que cantan (15 minutes)

### Narrative

The purpose of this activity is for students to complete and solve numberless Add To, Result Unknown and Take From, Result Unknown story problems. The story problems are about adding and subtracting 1, but they do not give a starting number and therefore highlight that adding 1 to any number gives the next number in the count sequence while subtracting 1 from any number gives the previous number in the count sequence. While the kindergarten standards only ask students to solve story problems with a result of up to 10, students may choose larger numbers for their problems.

Students may benefit from having the story problems in this activity read aloud multiple times.

Action and Expression: Internalize Executive Functions. Invite students to plan a strategy, including the number they are choosing for the missing number.
Supports accessibility for: Conceptual Processing, Organization

### Required Materials

Materials to Gather

### Launch

• Give students access to connecting cubes and 10-frames.
• “Algunos estudiantes estaban cantando. Después, vino 1 estudiante más a cantar con ellos. ¿Cuántos estudiantes están cantando ahora?” // “Some students were singing. Then 1 more student came to sing with them. How many students are singing now?”
• “¿Qué observan? ¿Qué se preguntan?” // “What do you notice? What do you wonder?” (Students were singing. Another student came to sing. How many students were singing? How many students are singing now?)
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share and record responses.

### Activity

• “Al problema-historia le hace falta el primer número. Llenen el espacio en blanco con un número y cuéntenle el problema-historia a su pareja. Muestren cómo pensaron. Usen objetos, dibujos, números o palabras” // “The story problem is missing the first number. Fill in a number and tell the story problem to your partner. Show your thinking using objects, drawings, numbers, or words.”
• 4 minutes: partner work time
• Repeat the steps, including noticing and wondering, with the second story problem.

### Student Facing

1. __________  estudiantes estaban cantando.
Después, vino 1 estudiante más a cantar con ellos.
¿Cuántos estudiantes están cantando ahora?

Muestra cómo pensaste. Usa objetos, dibujos, números o palabras.

_______________

2. __________ estudiantes estaban cantando.
Después, 1 estudiante dejó de cantar y se fue a su casa.
¿Cuántos estudiantes están cantando ahora?

Muestra cómo pensaste. Usa objetos, dibujos, números o palabras.

_______________

### Activity Synthesis

• Invite a student to share a story for the first problem. (There were 8 students singing. Then 1 more student came to sing with them. How many students are singing now?)
• “¿Cuántos estudiantes están cantando ahora? ¿Cómo lo saben?” // “How many students are singing now? How do you know?” (9 because 9 is 1 more than 8. 9 comes after 8 when we count.)
• “¿Y si había 9 estudiantes cantando y vino 1 más a cantar con ellos? ¿Cuántos estudiantes están cantando ahora? ¿Cómo lo saben?” // “What if there were 9 students singing and 1 more came to sing with them? How many students are singing now? How do you know?” (10. 10 is 1 more than 9.)

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

### Narrative

The purpose of this activity is for students to choose from activities that offer practice with number and shape concepts. Students choose from 5 centers introduced in previous units. Students can choose to work at any stage of the centers.
• Less, Same, More
• Math Fingers
• Tower Build
• Math Stories
• Which One
Students will continue to choose from these centers in upcoming lessons. Keep the materials from each center organized to use each day.

### Required Materials

Materials to Gather

### Required Preparation

• Gather materials from:
• Less, Same, More
• Math Fingers
• Tower Build
• Math Stories
• Which One

### Launch

• Groups of 2
• “Hoy vamos a escoger centros de los que ya conocemos” // “Today we are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Piensen qué les gustaría hacer primero” // “Think about what you would like to do first.”
• 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.

Menos, lo mismo, más

Dedos matemáticos

Construcción de torres

Historias matemáticas

¿Cuál es?

### Activity Synthesis

• “¿Qué pueden hacer cuando hay un problema de matemáticas o un centro sobre el que no están seguros?” // “What can you do when there is a math problem or center that you’re not sure about?”

## Lesson Synthesis

### Lesson Synthesis

“Hoy trabajamos con problemas-historia en los que una cosa se suma o en los que una cosa se resta, o se quita” // “Today we worked with story problems where one thing is added or one thing is subtracted, or taken away.”

“Cuando le suman 1 a un número, ¿qué número obtienen?” // “When you add 1 to a number, which number do you get?” (The next number when we count, the number that is one more)

“¿Alguien puede compartir un ejemplo de cuándo hicieron eso hoy?” // “Can someone share an example of when they did that today?”

“Cuando le quitan 1 a un número, ¿qué número obtienen?” // “When you take away 1 from a number, which number do you get?” (The one before the number when we count, the number that is one less, the number you say when you count backward)