# Lesson 14

Expresiones y problemas-historia

## Warm-up: Conteo grupal: Contemos hacia adelante (10 minutes)

### Narrative

The purpose of this warm-up is to count on from a given number. As students count, point to the numbers posted so that students can follow along. To support students as they learn to count on, consider asking “¿Cuál número va después del 3?” // “What number comes after 3?” or providing a running start by counting “1, 2, 3…” and having students continue the count.

### Launch

• “Contemos hasta 10” // “Let’s count to 10.”
• Count to 10.

### Activity

• “Ahora, empecemos en el número 3 y contemos hasta 10” // “Now start at the number 3 and count to 10.”
• Count on from 3 to 10.
• Repeat 3–4 times starting with other numbers within 10.

### Activity Synthesis

• “Podemos empezar a contar desde números diferentes al 1. Cuando contamos hacia adelante, pensamos en qué número va después” // “We can start counting at numbers other than 1. When we count on, we think about what number comes next when we count.”

## Activity 1: Expresión para un problema-historia (10 minutes)

### Narrative

The purpose of this activity is for students to explain how a subtraction expression represents a story problem (MP2). Students connect the expression to the story problem and then solve the story problem. Students will be introduced to equations in a later unit.

MLR8 Discussion Supports. Invite students to use connecting cubes or counters with verbal descriptions to explain what happened in the story problem.

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• “Cuéntenle a su compañero lo que ocurrió 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.
• Write the expression $$10 - 6$$.
• “¿Cómo muestra esta expresión lo que ocurre en el problema-historia?” // “How does this expression show what happens in the story problem?”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share responses.

### Activity

• “Muestren cómo pensaron. Usen dibujos, números, palabras u objetos” // “Show your thinking using drawings, numbers, words, or objects.”
• 2 minutes: independent work time
• 2 minutes: partner discussion

### Student Facing

Había 10 personas montando en bicicleta en el parque.

Luego, 6 de las personas dejaron de montar en bicicleta para ir a almorzar.

¿Cuántas personas están montando en bicicleta ahora?

### Activity Synthesis

• Write “$$10 - 6$$.”
• “¿Qué representa el 10 en el problema-historia? ¿Qué representa el 6?” // “What does the 10 represent in the story problem? What does the 6 represent?”
• “10 quitando 6 es 4. Podemos escribir eso como $$10 - 6$$ es 4” // “10 take away 6 is 4. We can write that as $$10 - 6$$ is 4.”

## Activity 2: ¿Cuál expresión? (10 minutes)

### Narrative

The purpose of this activity is for students to choose expressions that represent story problems (MP2).

Representation: Develop Language and Symbols. Synthesis: Students may benefit from comparing the two problems and identifying what is different about what happened in the story and the expression that represents the story. Make connections between Lin putting more rocks in her jar and the addition symbol in the expression and the kids that left to go jump rope and the subtraction symbol in the expression.
Supports accessibility for: Visual-Spatial Processing, Conceptual Processing

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• “¿Cuál expresión muestra lo que ocurrió en el problema-historia? Cuéntenle a su compañero cómo lo saben” // “Which expression shows what happened in the story problem? Tell your partner how you know.”

### Activity

• 30 seconds: quiet think time
• 2 minutes: partner discussion
• Share responses.
• Repeat the steps with the second story problem and expressions.

### Student Facing

1. Había 2 piedras en el tarro de Lin.
En el parque, Lin puso 4 piedras más dentro del tarro.
¿Cuántas piedras hay en el tarro de Lin ahora?

$$3 + 3$$

$$6 - 2$$

$$2 + 4$$

2. Había 8 niños jugando rayuela.
3 de los niños se fueron a saltar la cuerda.
¿Cuántos niños están jugando rayuela ahora?

$$8 + 3$$

$$3 - 3$$

$$8 - 3$$

### Student Response

If students match the second story problem with an expression other than $$8 - 3$$, consider asking:

• “¿Puedes contarme lo que ocurre en el problema-historia?” // “Can you tell me what is happening in the story problem?”
• “¿Se está agregando algo o se está quitando algo en el problema-historia? ¿Cómo te puede ayudar esto a descubrir cuál expresión le corresponde?” // “Is something being added or taken away in the story problem? How can that help you figure out which expression matches?”

### Activity Synthesis

• Display $$8 + 3$$ and $$8 - 3$$. If needed, reread the second story problem.
• “¿Cuál expresión escogieron? ¿Cómo supieron cuál expresión escoger?” // “Which expression did you choose? How did you know which expression to choose?” ($$8 - 3$$. Some of the kids left, so I chose the one with the minus sign.)
• Display $$8 - 3$$.
• “Usen esta expresión para contarle a su compañero lo que ocurrió en la historia” // “Use this expression to tell your partner what happened in the story.”

## Activity 3: Centros: Momento de escoger (25 minutes)

### Narrative

The purpose of this activity is for students to choose from activities that offer practice writing numbers and telling and solving story problems. Students choose from any stage of previously introduced centers.

• Number Race
• Math Stories
Students will choose from these centers throughout the section. Keep materials from these centers organized to use each day.

### Required Materials

Materials to Gather

### Required Preparation

• Gather materials from:
• Number Race, Stage 1
• Math Stories, Stages 1 and 2

### Launch

• “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
• “Escojan qué les gustaría hacer ahora” // “Choose what you would like to do next.”
• 10 minutes: center work time

### Student Facing

Escoge un centro.

Carrera con números

Historias matemáticas

### Activity Synthesis

• “De los problemas-historia que su compañero les contó, ¿cuál fue su favorito? ¿Por qué fue su favorito?” // “What was your favorite story problem that your partner told you? Why was it your favorite?”

## Lesson Synthesis

### Lesson Synthesis

There were 10 people riding bikes in the park.
Then 6 of the people stopped riding to have lunch.
How many people are riding bikes now?

Display $$10 + 6$$.

“Han dice que $$10 + 6$$ corresponde a este problema-historia porque primero hay 10 personas y luego hay 6 personas. ¿Qué piensan?” // “Han says that $$10 + 6$$ matches this story problem because there are 10 people first and then there are 6 people. What do you think?” (It doesn't match. 6 people stopped riding bikes, so you need to use $$10 - 6$$.)