Lesson 10

This Number Talk is designed to develop fluency with addition and subtraction of multi-digit numbers. This warm-up also gives students a chance to reason about numbers beyond 1,000. The understanding elicited here will be helpful later in the unit and throughout grade 4 when students add and subtract fluently using the standard algorithm.

• 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.

• “¿Qué partes del número cambian cuando sumamos 75?” // “Which parts of the number change when we add 75?” (Just the hundreds, tens and ones.)
• “¿Cómo sabemos, sin sumar, si algunos de los dígitos de un número van a cambiar?” // “How do we know without adding if digits in a number are going to change?” (Because we are not adding more than 10 tens to any of the numbers and there's only 6 hundreds, we know the thousands are not going to change.)

In this activity, students make sense of the relationships between the values of the same digit in different numbers, and write multiplication and division equations to represent these relationships.

As they complete and analyze the table, students recognize that the value of the digit in one row is ten times as much as the value of the digit in the row below. Students work to articulate these relationships precisely, using words and equations, and receive feedback from their peers on the equations they are writing. During the synthesis, students discuss why a multiplication or a division equation can be used to represent the same relationship.

When students express place value relationships with multiplication and division they observe structure in the place values (MP7). When they help one another improve their explanations, they critique each other's reasoning (MP3).

This activity uses MLR1 Stronger and Clearer Each Time. Advances: reading, writing.

• Groups of 2

MLR1 Stronger and Clearer Each Time

• 5 minutes: independent work
• “Compartan con su compañero su respuesta al segundo problema. Por turnos, uno habla y el otro escucha. Si es su turno de hablar, compartan sus ideas y lo que han escrito hasta ese momento. Si es su turno de escuchar, hagan preguntas y comentarios que ayuden a su compañero a mejorar su trabajo” // “Share your response to the second problem with your partner. Take turns being the speaker and the listener. If you are the speaker, share your ideas and writing so far. If you are the listener, ask questions and give feedback to help your partner improve their work.”
• 3–5 minutes: structured partner discussion
• Repeat with 2–3 different partners.
• If needed, display question starters and prompts for feedback.
  • “¿Pueden dar un ejemplo que ayude a mostrar . . . ?” // “Can you give an example to help show . . . ?”
  • “¿Pueden usar la palabra _____ en su explicación?” // “Can you use the word _____ in your explanation?”
  • “Ajusten su borrador inicial basándose en los comentarios que les hicieron sus compañeros” // “Revise your initial draft based on the feedback you got from your partners.”
• 2–3 minutes: independent work time
• Monitor for students who write a multiplication and division equation to represent the relationship between the values of the 8 in two different numbers.

• Select 1-2 students to share a multiplication and a division equation.

In this activity, students use the context of money to deepen their understanding of the relationship between the value of digits in different places—by counting equal groups of tens, hundreds, thousands, and ten-thousands. Writing the value of each stack of bills reinforces the “ten times” relationship between the place values, which in turns supports students in writing multiplication and division equations (MP7).

If play money is available, consider creating a counting collection and asking students to organize each stack and write equations to represent the stacks of bills. Ultimately, students would evaluate the expressions used by different groups and discuss the reasoning behind each equation.

• Groups of 2
• “Tómense un minuto para leer las instrucciones de la actividad y explicárselas a su compañero” // “Take a minute to read over the directions to the activity and explain them to a partner.”

• 5 minutes: independent work
• 10 minutes: partner work
• As students work, monitor for the different ways they describe the relationship between the stack of bills.
  • Each stack has the same number of bills but have different values.
  • The value of some stacks can be multiplied by ten to have the same value as another stack.

Students may be able to write an equation to represent the relationship between digits in the hundreds and thousands but get stuck when writing equations that represent the relationships between digits in larger place values. Consider asking students to describe the relationship between 1,000 and 10,000 by asking:

• “¿Cuántos grupos de 1,000 se necesitan para formar un grupo de 10,000?” // “How many groups of 1,000 are needed to create a group of 10,000?”
• “¿Cómo pueden usar esta manera de razonar para pensar en la relación que hay entre 2,000 y 20,000?” // “How might you use this reasoning to think about the relationship between 2,000 and 20,000?”

• See lesson synthesis.