# Lesson 7

Sumemos y restemos hasta 1,000

## Warm-up: Cuál es diferente: Sumemos y restemos hasta 100 (10 minutes)

### Narrative

This warm-up prompts students to carefully analyze and compare expressions. In making comparisons, students have a reason to use language precisely. Listen for the language students use to describe and compare the expressions with a focus on descriptions of the digits, the operations, place value, and whether or not units may be composed or decomposed when using methods based on place value (MP6).

### Launch

• Groups of 2
• Display the image.

### Activity

• “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
• 2–3 minutes: partner discussion
• Record responses.

### Student Facing

¿Cuál es diferente?

1. $$74 - 23$$
2. $$24 + 37$$
3. 4 decenas + 2 unidades + 3 decenas + 7 unidades
4. $$60 + 19$$

### Activity Synthesis

• “Encontremos una razón por la que cada expresión es diferente” // “Let’s find one way each expression doesn’t belong.”

## Activity 1: ¿Cuál prefieren encontrar? (20 minutes)

### Narrative

The purpose of this activity is for students to add and subtract within 1,000. Students begin the activity by analyzing different expressions without adding or subtracting to determine which values they think would be the least and most challenging to find. In the synthesis, students share different reasons why sums and differences were chosen to be “least” and “most challenging” and different methods for finding the values of the expressions.

Although students may have many different reasons for why they think expressions are more or less challenging to find, the synthesis focuses on reasons based on composing or decomposing units. Discussing whether students will compose or decompose units will support students in fluently finding sums and differences within 100 in the next activity.

This activity uses MLR8 Discussion Supports. Advances: speaking

• Groups of 2

### Activity

• “Sin encontrar el valor de ninguna suma ni diferencia, lean cada expresión y marquen las dos expresiones que piensan que son las más retadoras” // “Without finding the value of any of the sums or differences, read each expression and circle the two you think would be the most challenging to find the value of.”
• 3 minutes: independent work time
• “Escojan una de las expresiones que marcaron y encuentren su valor. Luego, escojan otras 2 expresiones y encuentren su valor” // “Choose one of the expressions you circled and find the value. Then choose 2 other expressions and find their value.”
• 4 minutes: independent work time
• “Compartan su trabajo con su compañero. Expliquen por qué escogieron esas expresiones y el método que usaron para encontrar los valores” // “Share your work with your partner. Explain why you picked your expressions and the method you used to find the values.”
MLR8 Discussion Supports
• Display sentence frames to support students when they explain their strategy:
• “Escogí _____ porque . . .” // “I picked _____ because . . . .”
• “Primero, yo _____ porque . . .” // “First, I _____ because . . . .”
• “Observé _____, entonces yo . . .” // “I noticed _____ so I . . . .”
• 4 minutes: partner discussion

### Student Facing

A
$$102 + 341$$

G
$$64 + 37$$

B
$$385 - 124$$

H
$$302 - 198$$

C
$$611 - 45$$

I
$$73 - 27$$

D
$$87 + 38$$

J
$$685 + 279$$

E
$$571 - 268$$

K
$$320 + 509$$

F
$$885 - 142$$

L
$$53 + 52$$

1. Marca 2 sumas o diferencias que pienses que son las más retadoras. Encuentra el valor de una de estas expresiones. Muestra cómo pensaste.
2. Escoge otras 2 expresiones y encuentra los valores. Muestra cómo pensaste.

### Activity Synthesis

• Poll the class. For each expression, ask students to “¿La expresión fue retadora? Levanten un dedo si no les pareció retadora, dos dedos si les pareció un poco retadora o tres dedos si les pareció la más retadora” // “Show one finger if the expression was not challenging, two fingers if it was a little challenging, or three fingers if it was the most challenging to find.”
• Consider displaying:
• A, D, E, F, H, J
• Stop for any expressions where there is a mix of ratings.
• “¿Por qué sienten que esta expresión es más retadora?” // “Why did you feel this expression is more challenging?”
• “¿Quién puede decirnos por qué esta expresión fue menos retadora?” // “Who can share why this expression was less challenging?”
• For expressions where most or all students felt the expression was most challenging, select students to share different methods for finding the value.
• “Todas las expresiones que sintieron que fueron las más retadoras pueden volverse menos retadoras si practican y si usan lo que saben sobre el valor posicional” // “All the expressions you felt were most challenging can become less challenging with practice and using what you know about place value.”

## Activity 2: Sumemos y restemos hasta 100 (15 minutes)

### Narrative

The purpose of this activity is for students to fluently find sums and differences within 100. Students should be encouraged to use whatever method makes the most sense to them, including mental strategies. In the synthesis, students reflect on which values were least and most challenging to find.

Engagement: Provide Access by Recruiting Interest. Provide choice and autonomy. Provide access to white boards and markers, or colored pencils and large paper for students to create a poster of their work. Encourage number lines or notation that show student thinking. If time allows, let students view each other’s strategies in solving the same problems. Focus on the differences in strategies, but the similarities in answers.
Supports accessibility for: Attention, Organization, Social-Emotional Functioning

• Groups of 2

### Activity

• “Ahora practiquemos cómo sumar y restar con fluidez” // “Now let’s practice adding and subtracting with fluency.”
• “Encuentren el valor de estas expresiones. Usen cualquier método que tenga sentido para ustedes. No tienen que usar representaciones ni símbolos para mostrar lo que hicieron, pero prepárense para compartir cómo encontraron cada valor” // “Find the value of these expressions. Use any method that makes sense to you. You do not need to show your work with a representation or symbols, but be ready to share how you found each value.”
• 5 minutes: independent work time
• “Compartan con su compañero cómo pensaron. Escojan una suma o una diferencia que ambos hayan sentido que fue menos retadora y una suma o una diferencia que ambos hayan sentido que fue más retadora” // “Share your thinking with your partner. Find 1 sum or difference that you both felt was the less challenging and 1 sum or difference that you both feel was more challenging.”
• 3 minutes: partner discussion
• Monitor for students who:
• describe why A, C, E, or G are less challenging because they do not need to compose or decompose
• describe why B, F, H, or J are more challenging because units are composed or decomposed or because they need to do more steps (in their head or on paper)
• describe why D, I, K, or L were less challenging because they saw ways to count up or back quickly, make a 10, or used facts they know

### Student Facing

1. Encuentra el valor de cada expresión.

A
$$31 + 25$$

G
$$95 - 81$$

B
$$43 + 28$$

H
$$37 + 55$$

C
$$89 - 22$$

I
$$25 + 25$$

D
$$40 - 28$$

J
$$63 - 19$$

E
$$15 + 72$$

K
$$72 - 68$$

F
$$85 - 37$$

L
$$21 + 59$$

2. Escoge una expresión que te haya parecido menos retadora. Explica.
3. Escoge una expresión que te haya parecido más retadora. Explica.

### Student Response

If students find the value for an expression that is not correct or get stuck when finding a value, consider asking:

• “¿Qué sabes sobre los números de esta expresión?” // “What do you know about the numbers in this expression?”
• “¿Qué métodos que vimos en lecciones anteriores puedes usar para encontrar el valor?” // “What methods from previous lessons could you use to find the value?”

### Activity Synthesis

• Share 1–2 sums students felt were least challenging.
• Invite previously identified students to share methods they used for finding the sums or differences mentally.
• Share 1–2 sums that students felt were most challenging.
• Invite previously identified students to share different methods for finding the values.

## Lesson Synthesis

### Lesson Synthesis

“Hoy practicamos sumas y restas de números de tres dígitos. También practicamos cómo sumar y restar números de dos dígitos con fluidez” // “Today we practiced adding and subtracting with three-digit numbers. We also practiced fluently adding and subtracting two-digit numbers.”

“¿Cuándo observaron que era más fácil encontrar los valores de las expresiones?” // “When did you notice it was easier to find the values of expressions?” (If I noticed I could just add or subtract the hundreds, tens, and ones without any extra steps.)

“De los métodos que compartieron otros estudiantes hoy, ¿cuáles quisieran probar al sumar o al restar?” // “What methods did you hear from other students today that you want to try when adding or subtracting?”