The purpose of this activity is for students to add 2 two-digit numbers within 100 and show their thinking with equations. Although some students may write each step of their thinking with equations, it is not required that they do so. Students can write one equation that shows the sum and represent their method in their drawings. In the Activity Synthesis, students present their method verbally to a new partner.

This activity uses MLR8 Discussion Supports. Advances: listening, speaking, conversing

• Display sentence frames to support students when they explain their method as equations:
  • “Primero, yo _____ porque . . .” // “First, I _____ because . . .”
  • “Observé ______, entonces yo . . .” // “I noticed _____ so I . . .”
• “Van a explicarle su método a otro estudiante de la clase. Practiquen con su pareja lo que van a decir. Usen estas frases ejemplo como ayuda” // “You are going to explain your method to another student in the class. Practice what you will say with your partner. Use these sentence starters to help you.”
• 3 minutes: partner discussion
• “Encuentren a un nuevo compañero y explíquenle su método” // “Find a new partner and explain your method.”
• 2 minutes: partner discussion

The purpose of this activity is for students to use what they know about the base-ten structure of numbers to create different expressions. Students use place value reasoning to create expressions with the smallest and largest values and expressions that may or may not require composing a ten when adding using methods based on place value (MP7). In the Activity Synthesis, students explain how they reasoned about whether or not a new ten could be composed just by looking at the addends (MP3). Although some students may complete the activity without finding any sums, others may need to find partial sums or complete sums in order to explain what happens when adding.

• Invite a previously identified student to share their expression that does not require making a new ten.
• “¿Podrían usar otros números? ¿Cómo lo saben?” // “Are there other numbers you could use? How do you know?"
• Invite a student to share who found 2 numbers that make a ten without finding the sums.
• “¿Podrían usar otros números? ¿Cómo lo saben?” // “Are there other numbers you could use? How do you know?"

The purpose of this activity is for students to relate adding within 100 to real-world contexts. In previous lessons and activities, students have used different methods to add within 100. In this activity, students solve problems that help them see when this type of addition is used in people’s lives. This activity is optional because it is an opportunity for extra practice that not all classes may need.

When students connect the quantities in the story problem to an equation, they reason abstractly and quantitatively (MP2).

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