Lesson 3

The purpose of this Number Talk is to elicit strategies and understandings students have for adding within 100. These understandings help students develop fluency and will be helpful later in this lesson when students add two-digit numbers using methods based on place value.

• Display one expression.
• “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.

• “How can \(23 + 31\) help you solve \(33 + 41\)?” (The tens are changing again. In \(33 + 41\), you are adding 2 tens total, so the sum of \(23 + 31\) increases by 20. \(54 + 20 = 74\).)

The purpose of this activity is for students to make sense of the first step of addition methods and then finish finding the sum. They write equations to represent their thinking. In the synthesis, students have opportunities to share how they represented a method with equations and connect the representations using their understanding of place value (MP7).

• Groups of 2
• Give students access to connecting cubes in towers of 10 and singles.

• Read the task statement.
• 7 minutes: partner work time
• Monitor for a student who writes equations to represent how each student can find the value and can explain their thinking.

If students take new steps that do not lead to a value of 86, consider asking:

• “What do you think Lin (or Han) should do next? Why?”
• “What did Lin (or Han) do first? How could you show what they did with connecting cubes?”
• “What do they need to do next? How do you know?”
• “How could you represent the next step with an equation?”

• Invite previously identified students to share their equations for Lin's work and then Han's work.
• “How are these equations the same? How are they different?” (They both got the same sum. They both add tens and ones. The first one breaks apart both numbers and adds tens and tens and ones and ones. The second one starts with 54 and adds the tens then the ones.)

The purpose of this activity is for students to find the sum of 2 two-digit numbers and represent their thinking with equations. Students then orally explain their steps to a partner and how the equations they wrote match their steps. Partners listen and then practice restating what they heard their partner say. Restating what a partner has said helps ensure students listen for understanding as their partner explains their thinking. Students have multiple opportunities to explain their thinking and the thinking of a partner and revise their language for clarity (MP3, MP6).

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

• Groups of 2
• Give students access to connecting cubes in towers of 10 and singles. 

• Read the task statement.
• 5 minutes: independent work time
• Monitor for students using different methods in order to make partnerships of students who found the value in different ways.
• “Now you are going to explain to your partner how you found the value of the sum. Use your drawings or connecting cubes to explain your steps. Also explain how the equations you wrote match each step you took.”

MLR8 Discussion Supports

• “After your partner explains their method, restate what you heard from your partner.”
• Display the sentence frame: “I heard you say . . .”
• “Ask your partner if you restated their thinking accurately.“
• 8 minute: partner discussion

• “What was most difficult about restating your partner’s thinking? What helped you make sense of your partner’s thinking and restate it?”