Lesson 5

The purpose of this Number Talk is to elicit strategies and understandings students have for adding a one-digit number to a two-digit number. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to add within 50.

• 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 una suma con números grandes, ¿cómo les ayuda buscar maneras de formar 10?” // “How does looking for ways to make 10 help to find the value of the sum with larger numbers?” (You can make a ten with the ones and then add the other tens back on. \(38 + 6\), \(8 + 2 = 10\), \(10 + 30 + 4 = 44\).)

The purpose of this activity is for students to learn stage 3 of the How Close center which was introduced in grade 1. In this stage, each student picks 7 cards and chooses 4 of them to create 2 two-digit numbers. Each student adds the numbers and the student whose sum is closest to 100 wins a point for the round. It is recommended that at this point in the year, students begin with a target number of 50 instead of 100 in this stage.

If students are not yet able to make 2 numbers that get close to 50, encourage them to choose 2 cards, make a 2 digit number and represent the number with cubes. Then determine how many more cubes they need to get to 50 and choose the 2 cards that will get closest to that number.

• Groups of 2
• Give one set of digit cards to each group.
• “Hoy vamos a jugar otro juego de ‘Qué tan cerca’. Esta vez jugaremos ‘Cerca de 50’” // “Today we are going to play another game of How Close. This time we will play Close to 50.”
• Display the digit cards at the top of the student page.
• “Empezamos con 7 tarjetas otra vez. Piensen qué tarjetas escogerían para formar 2 números de dos dígitos que tengan una suma cercana a 50” // “We start with 7 cards again. Think about what cards you would choose to make 2 two-digit numbers that have a sum close to 50.”
• 1 minute: quiet think time
• 2-3 minutes: partner work time
• Share responses.
• “Después de formar los números de dos dígitos, escriban una ecuación que muestre la suma” // “After you make your two-digit numbers, you will write an equation showing the sum.”
• Demonstrate writing an equation on the recording sheet.
• “Ahora, vean quién hizo la suma más cercana a 50. Hablen con su pareja sobre cómo podrían saberlo” // “Now, we see whose sum is closer to 50. Talk to your partner about how you could figure it out.” (You can count up or back from 50 and see whose number is closer.)
• 30 seconds: quiet think time
• 1 minute: partner discussion
• “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 pareja” // "Now play How Close with your partner."
• 10 minutes: partner work time

• Display digit cards from the student page.
• “Diego formó el número 38. ¿Qué número podría formar Diego ahora para acercarse a 50?” // “Diego made the number 38. What number could Diego make next to get close to 50?”

In this activity, students find the value of sums with larger numbers using any method that makes sense to them. They may represent their thinking using connecting cubes, drawings, equations, or words. Monitor for the ways students use methods based on place value, including the language they use to describe composing a ten when adding tens and tens and ones and ones (MP3, MP6).

• Create connecting cubes in towers of 10 and singles.

• Groups of 2
• Give students access to connecting cubes in towers of 10 and singles.
• “Ahora vamos a sumar números más grandes. Piensen cómo pueden mostrar lo que pensaron para que otros puedan entender” // “Now we are going to add larger numbers. 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 students who:
  • Add by place value (\(27 + 15\), \(20 + 10 = 30\), \(7 + 5 = 12\), \(30 + 12 = 42\))
  • Decompose 1 number to make a 10, then add the rest (\(27 + 15\), \(27 + 3 = 30\), \(30 + 12 = 42\))

• Display \(27 + 15\).
• Select previously identified students to share.