Lesson 8

The purpose of this Number Talk is to elicit strategies and understandings students have for adding one-digit and two-digit numbers. When recording students’ thinking, record using expressions that match student methods. For example as a student is explaining \(45 + 7\), you may write \(45 + 5 + 2\).

• 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.

• “¿En qué se parecen \(68 + 2\) y \(45 + 5\)?” // “How are \(68 + 2\) and \(45 + 5\) alike?” (They both have a value that is a multiple of 10.)
• “¿En qué se parecen \(68 + 3\) y \(45 + 7\)?” // “How are \(68 + 3\) and \(45 + 7\) alike?” (The ones in both expressions make more than ten, so we can compose a ten to help us add.)

The purpose of this activity is for students to learn stage 2 of the Target Numbers center. Students start with 25, choose a number card and decide whether to add that number of tens or ones. Students play six rounds and the student who gets as close to 95 as possible without going over is the winner.

• Groups of 2
• Give each group a set of number cards, two recording sheets, and access to connecting cubes in towers of 10 and singles.
• “Saquen las tarjetas que muestren 0 o 10 y pónganlas aparte” // “Take out all of the cards that show 0 or 10.”
• “Vamos a aprender una nueva forma de jugar ‘Números objetivo’. Esta vez, su meta es acercarse lo más que puedan a 95 sin pasarse. Solo tienen 6 turnos. En cada turno, pueden decidir si quieren sumarle decenas o sumarle unidades a su número. Juguemos una ronda juntos. Cada compañero empieza en 25” // “We are going to learn a new way to play Target Numbers. This time, your goal is to get as close to 95 as you can, without going over. You only get 6 turns. On each turn, you get to decide whether you want to add tens or ones to your number. Let’s play a round together. Each partner starts at 25.”
• Demonstrate drawing a number card.
• “Tomé un [4]. ¿Debería sumar 4 unidades o sumar 4 decenas? ¿Por qué?” // “I drew a [4]. Should I add 4 ones or 4 tens? Why?” (You can add 4 tens because that will give you 65. You still have 5 rounds to get to 95. You can add 4 ones to make 29. That gives you more time to add tens.)
• 30 seconds: quiet think time
• 30 seconds: partner discussion
• Share responses.
• “Voy a sumar 4 decenas: 2 decenas y 4 decenas es 6 decenas. Así que mi suma es 65” // “I’m going to add 4 tens, 2 tens and 4 tens is 6 tens. So my sum is 65.”
• “Cuando mi compañero y yo estemos de acuerdo en la suma, el compañero que tomó la tarjeta de números escribe una ecuación. Como 25 ya se llenó para mí, voy a escribir el número como decenas (o unidades) y la suma” // “Once my partner and I agree on the sum, the partner who drew the number card records an equation. Since 25 is already filled in for me, I will record the number as tens (or ones) and the sum.”
• Demonstrate completing the equation.
• “Después de escribir mi ecuación, la suma se vuelve el número con el que empiezo la siguiente ronda. Lo escribo como el primer número de la ecuación que sigue” // “After I write my equation, the sum becomes my starting number for the next round, so I write it in as the first number in the next equation.”
• If needed, play another round with the class.
• “Por turnos, tomen las tarjetas de números, encuentren la suma y escriban la ecuación. Cada jugador juega 6 rondas. Gana el jugador que quede más cerca de 95 sin pasarse” // “Take turns drawing the number card, finding the sum and writing an equation. Each player plays 6 rounds. Whoever gets closest to 95 without going over is the winner.”

• 10 minutes: partner work time

• “Cuando toman una tarjeta de números, ¿cuál es su método para decidir si suman decenas o unidades?” // “When you draw the number card, what is your method for deciding whether to add that many tens or ones?” (I think about how close I am to 95. That helps me think about whether to add ones or tens.)

The purpose of this activity is for students to choose from activities that focus on adding within 100. Students choose from any stage of previously introduced centers.

• Target Numbers
• Number Puzzles
• Five in a Row

• Gather materials from previous centers:
  • Target Numbers, Stages 1 and 2
  • Number Puzzles, Stages 1-3
  • Five in a Row, Stages 1-5

• Groups of 2
• Display the student page.
• “Piensen qué les gustaría hacer primero” // “Think about which activity you would like to do first.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice.
• 10 minutes: center work time
• “Escojan qué les gustaría hacer ahora” // “Choose what you would like to do next.”
• 10 minutes: center work time
   

• “Digan una cosa que hayan aprendido o en la que hayan mejorado al trabajar en las actividades que escogieron” // “What is one thing you learned or got better at by working on the activities you chose?”

The purpose of this activity is for students to experience different contexts in which someone adds a two-digit and a one-digit number. This helps students see math in their world. If necessary, the context of each problem can be changed to something more familiar to the students. This activity is optional because it provides practice solving story problems with numbers larger than 20, which is not an expectation of students in grade 1. 

When students create representations and expressions for the context, they develop ways to model the mathematics of a situation and strategies for making sense of and persevering to solve problems (MP1, MP4).

• Groups of 2
• Give students access to connecting cubes in towers of 10 and singles.

• Read the task statement.
• 3 minutes: independent work time
• 3 minutes: partner discussion

• Invite students to share the methods used for each problem. Record equations to match each method.