The purpose of this activity is for students to analyze two different subtraction methods that are based on place value and connect the methods to equations. In previous lessons, students analyzed base-ten drawings like Lin’s where a student recognizes that a ten needs to be decomposed before they draw the blocks. Clare’s drawing represents a student who mentally subtracts tens from tens before drawing and then considers decomposing units. Students discuss how each method works and deepen their understanding of the properties of operations (MP7).

• Invite students to share the group of equations that match Lin's work and Clare’s work.
• “¿En qué se parecen estos métodos?” // “How are these methods the same?” (See Student Responses, second problem.)
• “¿En qué son diferentes los métodos?” // “How are the methods different?” (See Student Responses, third problem.)
• “¿Encontró Clare el valor de ? ¿Qué aprendieron sobre el método de ella?” // “Did Clare find the value of ? What did you learn about her method?” (Yes, she did because she did take away tens. I learned you can take away tens first and it doesn’t change the difference.)

The purpose of this activity is to analyze a subtraction method that is based on place value and connect it to equations. Students analyze the method and explain why they think it best matches one of the methods they saw in the previous activity. Then they practice subtraction using any method that makes sense to them. Monitor for different methods to share in the Synthesis, including students who show ways to subtract ones from ones first and those who subtract tens from tens first. 

• Invite 1–2 students to share their method for each difference. 
• Consider asking or inviting students to ask questions of students who share:
  • “¿Qué hicieron primero?” // “What did you do first?”
  • “¿Por qué escogieron esta representación?” // “Why did you choose this representation?”
  • “¿En qué se parece su método al método de _____?” // “How is your method like _____’s method?”