The purpose of this activity is for students to interpret base-ten diagrams that represent decomposing a unit when subtracting by place (MP2). Students analyze base-ten diagrams that show decomposing a hundred into 10 tens. They make connections between representing with base-ten blocks and base-ten diagrams, and between decomposing a hundred and decomposing a ten.

If students match an expression to a diagram that doesn't show the same value, consider asking:

• “¿Cómo emparejaste esta expresión con este diagrama?” // “How did you match this expression and diagram?”
• “¿Cómo muestra el diagrama cada número de la expresión?” // “How does the diagram show each number in the expression?”

• Invite students to share the expression that matches each diagram.
• “¿A qué tenían que prestarle atención cuando emparejaron cada diagrama con una expresión?” // “What did you have to look for as you matched each diagram to an expression?” (I had to look at the numbers to see where I needed to decompose a hundred or a ten. I saw that the first diagram shows no ones left over, without decomposing a ten. The second diagram shows ones left over, with decomposing a ten. The third diagram shows ones left over, without decomposing a ten.)

The purpose of this activity is for students to subtract by place and record their thinking. Students decompose either a ten or a hundred as they subtract. They should have access to base-ten blocks, but can represent their thinking in any way that makes sense to them. Throughout the activity, as students share their thinking with their peers, listen for the way they use place-value terminology and provide them with opportunities to revise their language for precision and clarity.

If students use only base-ten blocks and do not show their thinking with a diagram, equations, or words, consider asking:

• “¿Qué hiciste para encontrar el valor de esta diferencia?” // “What did you do to find the value of this difference?”
• “¿Cómo puedes usar un diagrama o una ecuación para mostrar de qué manera usaste los bloques?” // “How could you use a diagram or an equation to record how you used the blocks?”

• Invite previously identified students to share how they found the value of each difference.
• After each student shares, consider asking:
  • “¿_____ descompuso para restar? ¿Por qué? ¿Cómo pueden usar el diagrama que hizo para saberlo?” // “Did _____ decompose to subtract? Why? How can you use their diagram to tell?”
  • “¿En qué se parece el método de _____ para encontrar la diferencia al de ustedes? ¿En qué es diferente?” // “How is _____’s method for finding the difference the same as yours? How is it different?”
  • “¿Qué preguntas quieren hacerle a _____ sobre sus pasos o su representación?” // “What questions do you have for _____ about their steps or their representation?”