Lesson 9

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.

• 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

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

• “¿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?”

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.

• 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.”

• 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.

• “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.”

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.

• 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.

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

• “Van a resolver acertijos numéricos. Cada acertijo tiene cuatro pistas. Una de las pistas está sombreada y doblada. Dejen esa pista para el final. Lean las demás pistas y descubran juntos cuáles números se ajustan a las pistas. Cuando estén de acuerdo en los números que se ajustan a todas las pistas, lean la pista que está sombreada y doblada. Encuentren juntos la respuesta y escríbanla en su libro. Luego, pongan todas las pistas nuevamente en el sobre y prepárense para pasar al siguiente acertijo. Yo les diré cuándo pasar al siguiente” // “You are going to solve number riddles. Each riddle has four clues. One clue is shaded and folded. Keep this clue until last. Read the other clues and work together to figure out which numbers fit the clues. Once you agree on what numbers fit all the clues, read the shaded, folded clue. Work together to find the answer and write your answer in your book. Then put all the clues back in the envelope and get ready to move on to the next riddle. I will let you know when to move.”
• 20 minutes: partner work time

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