The purpose of this activity is for students to connect a subtraction method based on place value to representations on the number line. Students compare representations of a subtraction method using base-ten diagrams, equations, and number lines (MP2). They notice that, just like with base-ten blocks, they can count by tens first or by ones first on the number line to represent subtracting.

• “¿Puedes decirme más acerca de tu recta numérica? ¿Cómo supiste dónde empezar?” // “Can you tell me more about your number line? How did you decide where to start?”
• “¿Cómo se relaciona la recta numérica con tu diagrama en base diez?” // “How does the number line connect to your base-ten diagram?”

• Invite previously identified students to share.
• Display or record their methods.
• Consider asking each student:
  • “¿Cómo decidieron dónde empezar, cuántos saltos dar y la longitud de cada salto?” // “How did you decide where to start, how many jumps to make, and the length of each jump?”
• “¿En qué se parecen estos métodos? ¿En qué son diferentes?” // “How are these methods the same? How are they different?” (They started at 58. Some show subtracting tens first, and some show subtracting ones first. Some show subtracting the value of all the tens or all the ones. Some show subtracting each ten or each one.)
• “¿De qué manera la recta numérica les ayuda a ver en qué se parecen estos métodos?” // “How does the number line help you see how these methods are the same?” (It helps you see that it doesn't matter if you subtract tens first or ones first. They all show subtracting 24.) 

The purpose of this activity is for students to represent addition and subtraction within 100 on a number line. Students make connections to strategies based on counting on or back by place. The numbers in each subtraction equation are designed to elicit methods that do not require students to explicitly decompose a ten. For example, when finding the value of , students may first add on to make a ten (), then add on more tens to reach the total (). Others may see they can count back 2, then subtract the tens. In the Synthesis, students share their thinking and discuss how the number line helps them see how they can use what they know about the structure of counting sequences and what they know about tens and ones to add and subtract (MP7).

• Invite 2–3 previously selected students to share.
• Consider asking each student:
  • “¿Cómo decidieron dónde empezar?” // “How did you decide where to start?”
  • “¿Cómo decidieron cuánto sumar/restar primero?” // “How did you decide how much to add/subtract first?”
  • “¿De qué manera su recta numérica muestra el valor de la diferencia?” // “How does your number line show the value of the difference?”
• “¿Qué otras preguntas tienen sobre la recta numérica de _____?” // “What other questions do you have about _____'s number line?”
• “¿De qué manera la recta numérica les ayudó a entender el método de _____?” // “How does the number line help you make sense of _____'s method?”