# Lesson 9

Resolvamos acertijos numéricos

## Warm-up: Verdadero o falso: Afirmaciones de comparación (10 minutes)

### Narrative

The purpose of this True or False is to elicit strategies and understandings students have for comparing two-digit numbers. These understandings will be helpful later when students will need to be able to determine numbers that are greater than or less than a given number.

### Launch

• Display one statement.
• “Hagan una señal cuando sepan si la afirmación es verdadera o no, y puedan explicar cómo lo saben” // “Give me a signal when you know whether the statement is true and can explain how you know.”
• 1 minute: quiet think time

### Activity

• Share and record answers and strategies.
• Repeat with each equation.

### Student Facing

Prepárate para explicar tu razonamiento.

• $$65 > 35$$

• $$65 = 75 - 10$$

• $$65 > 35 + 30$$

### Activity Synthesis

• “¿Cómo pueden usar el número de decenas y de unidades que hay en cada lado para explicar sus respuestas?” // “How can you explain your answers by describing the number of tens and ones on each side?

## Activity 1: Un acertijo numérico (10 minutes)

### Narrative

The purpose of this activity is for students to use their understanding of place value to find a secret number in a number riddle. Initially, students are given clues that could have more than one secret number to encourage them to think about all the possibilities. Then, they receive a clue that allows them to figure out the secret number. Students will solve this type of riddle in small groups in the next activity.

### Launch

• Groups of 3
• Give students access to connecting cubes in towers of 10 and singles.
• “Vamos a resolver acertijos numéricos. Resolvamos uno juntos. Yo escogí un número secreto y les voy a dar tres pistas para ayudarles a identificar mi número” // “We are going to solve number riddles. Let's do one together. I have chosen a secret number and will give you three clues to help you identify my number.”
• Display the clues in the student book.
• “Usen las pistas para identificar qué números podrían ser mi número secreto. Las pistas no están en ningún orden específico. Pueden usar cualquier pista para empezar” // “Use the clues to identify numbers that could be my secret number. The clues aren’t in any specific order. You can use any clue to start.”

### Activity

• 4 minutes: small-group work time
• Monitor for groups of students who started with different clues.
• “¿Alguien sabe cuál es mi número secreto?” // “Does anyone know my secret number?” (It could be 34, 44 or 54 because they all fit the clue.)
• Display and read the new clue: “Mi número es la suma de 24 y 20” // “My number is the sum of 24 and 20.”
• “¿Cuál es mi número secreto?” // “What is my secret number?”
• Share responses.

### Student Facing

Mi número es menor que 60.

Mi número es mayor que 30.

¿Qué números se ajustan a estas pistas?

Número secreto: ___________

### Activity Synthesis

• “Como acabamos de ver, algunas veces hay varios números diferentes que se ajustan a las pistas hasta que obtenemos la última pista. Tengan esto en mente cuando resuelvan acertijos numéricos con su grupo en la siguiente actividad” // “As we just saw, sometimes many different numbers fit the clues until you get the last clue. Keep that in mind as you solve Number Riddles with your group in the next activity.”

## Activity 2: Más acertijos numéricos (25 minutes)

### Narrative

The purpose of this activity is for students to solve number riddles to find a secret number. Students work together to find the numbers that match the clues and justify why those numbers fit the clues (MP3). Then students read the last clue (shaded grey) and identify the secret number. Students rotate between riddles; it is also possible for students to remain in the same place and trade riddles.

MLR8 Discussion Supports. Prior to solving the riddles, invite students to make sense of the task and take turns sharing their understanding with their partner. Listen for and clarify any questions about the context.
Representation: Access for Perception. Provide appropriate reading accommodations and supports to ensure student access to written clues on Number Riddle Cards.
Supports accessibility for: Language, Social-Emotional Functioning

### Required Materials

Materials to Gather

Materials to Copy

• Number Riddle Cards, Spanish

### Required Preparation

• Create enough riddles from the Number Riddle Cards so each group of 2 students can have a different riddle. Fold the gray cards. Place each set of clues in a bag or envelope and label based on the letter of the riddle.

### Launch

• Groups of 2
• Give each group an envelope with a riddle and access to connecting cubes in towers of 10 and singles.

### Activity

• 20 minutes: partner work time

Números secretos

A: __________

B: __________

C: __________

D: __________

E: __________

F: __________

G: __________

H: __________

I: __________

J: __________

### Activity Synthesis

• Invite students to share the secret number for each riddle.

## Lesson Synthesis

### Lesson Synthesis

“Hoy resolvimos muchos acertijos numéricos. Estoy muy confundido con este y necesito su ayuda” // “Today we solved lots of number riddles. I’m really stumped on this one and need your help.“
Display the chart with only the first clue showing. “Mi número tiene más de 6 decenas” // “My number has more than 6 tens.“
“¿Cuál podría ser mi número secreto?” // “What could my secret number be?” (70, 75, 89, 91, any number from 70 to 120.)

Display the second clue: “Mi número es menor que 100” // “My number is less than 100.”
“¿Qué saben ahora sobre el número secreto?” // “Now what do you know about the secret number?” (We can cross out any of the numbers that are over 100.)

Display the third clue: “Mi número tiene 8 decenas” // “My number has 8 tens.”
“¿Cómo cambia esta pista el número que podría ser mi número secreto?” // “How does this clue change what my secret number could be?” (Now we know we can cross off all the numbers that don’t have 8 tens.)
“¿Cuál podría ser ahora mi número secreto?” // “What could my number be now?” (80–89)

Display the last clue: “Mi número es la suma de $$51 + 32$$” // “My number is the sum of $$51 + 32$$.”
“¿Cuál es mi número secreto? Expliquen cómo pensaron” // “What is my secret number? Explain your thinking.”