Lesson 13

The purpose of this Number Talk is to elicit strategies and understandings students have for adding to teen numbers. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to find the missing value in an equation with a teen number.

When students add ones to ones, they are making use of the structure of the base-ten number system (MP7).

• 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 does knowing \(4 + 3\) help you with \(14 + 3\)?” (You can add \(4 + 3\) and then add 10 more.)

The purpose of this activity is for students to solve a Take From, Change Unknown story problem using a method that makes sense to them. This is a challenging problem type for students because the amount that students are taking away or counting on is the unknown. The activity begins with a numberless and questionless story problem to help students understand the context and structure of the story problem. Students begin the activity by looking at the problem displayed, rather than in their books. The numbers 5, 10, and 15 are used so that the focus of the activity can be on making sense of the story problem, rather than the computation. Students may benefit from acting out the story.

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-color counters.
• Display and read the numberless and questionless story problem.
• “What do you notice? What do you wonder?”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Record responses.
• If needed, “What question could we ask?”

• “Turn the page and look at the next problem.”
• Read the complete story problem.
• 3 minutes: independent work time
• 2 minutes: partner discussion
• Monitor for students who:
  • Show 15 on the 10-frames and make 5 a different color to represent the students who are still standing. The student counts the remaining counters, or just see that there are 10. (\(15 - 5 = \boxed{10}\))
  • Draw 15 objects and cross out until there are 5 left. Count how many are crossed out. \(15 - \boxed{10} = 5\)
  • Take away 5 from 15 (14, 13, 12, 11, 10) (\(15 - 5 = \boxed{10}\)).

• Invite previously identified students to share.
• “How does this method show the story problem?” (I can see 15 for the number they started with. 10 is how many students sat down on the rug. 5 is how many students are still standing.)
• “Remember to put a box around your answer when you solve and write an equation.”

The purpose of the lesson is for students to solve a Take From, Result Unknown and a Take From, Change Unknown story problem. The story problems have the same numbers, which include a teen number, so that the focus can be on the structure of the story problems and the equations. In the activity synthesis students compare the structure of the problems and in the lesson synthesis, students make sense of equations that represent the story problems (MP2). 

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-color counters.

• Read the task statement.
• 4 minutes: independent work time
• “Share your thinking with your partner.”
• 2 minutes: partner discussion

• “How are the two story problems the same and different?” (They have the same numbers. In one of them we know how many to take away and in the other one we have to figure out how many to take away.)

The purpose of this activity is for students to choose from activities that offer practice adding and subtracting within 10. Students choose from any stage of previously introduced centers.

• Shake and Spill
• Compare
• Number Puzzles

• Gather materials from previous centers:
  • Shake and Spill, Stages 3-5
  • Compare, Stage 1
  • Number Puzzles, Stage 1

• Groups of 2
• “Now you are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Think about what you would like to do.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice. 
• 10 minutes: center work time

• Display twelve red counters and cover five yellow counters with a cup.
• “We are playing with seventeen counters. How many yellow counters are under the cup? How do you know?”