Lesson 4

The purpose of this Number Talk is to elicit strategies and understandings students have for making a ten to add. When students look for ways to decompose an addend to make 10, students look for and make use of the structure of numbers and the properties of operations (MP7). These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to add within 20.

• Display one expression.
• “Hagan una señal cuando tengan una respuesta y puedan explicar cómo la obtuvieron” // “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

• Record answers and strategy.
• Keep expressions and work displayed.
• Repeat with each expression.

• “Al encontrar el valor de las sumas, ¿cómo nos ayuda formar 10?” //“How does making 10 help in finding the value of the sums?” (It helped me because I was able to use facts I already know. I know \(7 + 3 = 10\) and I know \(10 + 3 = 13\).)

The purpose of this activity is for students to revisit stage 1 of the How Close center, which was first introduced in grade 1. Students pick 5 digit cards and then choose 3 to make an expression that has a value as close as possible to the target number, which is 20 in stage 1. Students may use a variety of strategies such as making a 10 to add two numbers or using the relationship between addition and subtraction to strategically choose 3 numbers (MP7).

• Groups of 2
• Give each group a set of cards. Have them remove the number 10 cards.
• Display the digit cards at the top of the student page.
• “Vamos a jugar un juego que se llama ‘¿Qué tan cerca?’. Juguemos una ronda juntos” // “We are going to play a game called How Close. Let’s play 1 round together.”
• “Miren las 5 tarjetas. Piensen cuáles 3 tarjetas sumarían para acercarse a 20” // “Look at the 5 cards. Think about which 3 cards you would choose to add together to get close to 20.”
• 1 minute: quiet think time
• 2-3 minutes: partner work time
• Share responses.
• “Después de escoger sus 3 tarjetas, escriban una ecuación que muestre la suma” // “After you choose your 3 cards, you will write an equation showing the sum.”
• Demonstrate writing an equation to show the sum of the 3 cards that get closest to 20.
• “Cuando tengan su ecuación escrita, compárenla con la de su compañero para ver quien encontró una suma más cercana a 20” // “When you have your equation written, compare it with your partner’s to see who found a sum closer to 20.”
• “Después, reemplacen las tarjetas que usaron y jueguen otra vez” // “Then you will replace the cards you used and play again.”

• “Ahora jueguen ‘¿Qué tan cerca?’ con su compañero” // "Now play How Close with your partner."
• 10 minutes: partner work time
• Monitor for students who:
  • try to make 10 and then add the greatest number possible to it
  • add the 2 greatest numbers and then look for the other number needed to make 20

• “¿Qué métodos usaron para encontrar una suma cercana a 20?” // “What methods did you use to find a sum close to 20?
• Invite previously selected students to share their strategies.

The purpose of this activity is for students to add and subtract within 20 using any method that makes sense to them. In the previous activity, students shared methods they used to add within 20. This activity gives students an opportunity to try some of the methods they discussed. In this activity, students also subtract within 20 and will discuss their methods in the synthesis.

• Groups of 2
• Give students access to connecting cubes.
• “Ahora vamos a sumar y restar hasta 20. Piensen en cómo pueden mostrar lo que pensaron para que los demás lo puedan entender“ // “Now we are going to add and subtract within 20. Think about how you can show your thinking so others can understand.”
• “Tienen tiempo para trabajar de manera independiente antes de compartir con un compañero cómo pensaron” // “You have time to work independently before sharing your thinking with a partner.”

• 5 minutes: independent work time
• 5 minutes: partner discussion
• Monitor for different methods used to find the value of \(17 - 9\). For example:
  • adding on to make 10 ( \(9 + 1 = 10\), \(10 + 7 = 17\), \(1 + 7 = 8\))
  • decomposing one number to get to 10 first ( \(17 - 7 = 10\), \(10 - 2 = 8\))

If students are counting all of the cubes by 1 or working with loose cubes, consider asking:
“¿Cómo usarías las torres de 10 como ayuda para encontrar las sumas o las diferencias?” // "How could you use towers of 10 to help you find the sums or differences?"

• Display 17 – 9.
• Select previously identified students to share their strategies.