Lesson 11

The purpose of this True or False is to elicit insights students have about composing teen numbers as a ten and some ones. This will be helpful later in the lesson when students add a single-digit number to a teen number within 20.

• Display one statement.
• “Give me a signal when you know whether the statement is true and can explain how you know.”
• 1 minute: quiet think time

• Share and record answers and strategy.
• Repeat with each equation.

• “Does anyone want to add on to _____ ’s reasoning?”
• “Did you determine if any of these were true or false without solving? How?” (I knew the first one without solving. Both had 10 + something, and one had a 4 and one had a 5, so they are not equal.)

The purpose of this activity is to elicit and discuss methods for adding a one-digit number to a teen number, within 20. Students are presented with a simple story problem type (Add To, Result Unknown) so discussion can focus on the methods students used to find the sum. Students represent and solve the problem in a way that makes sense to them (MP1). Some students may build the teen number, add counters and count all, while other students may count on from the teen number. Some students may see that the sum will still have 1 ten and just combine the ones. During the synthesis, students notice that when adding to teen numbers within 20, the unit of ten in the representation does not change—only the ones change (MP8).

• Groups of 2
• Give each group access to double 10-frames and connecting cubes or two-color counters.
• “Something that is common for people to collect is rocks. People collects lots of different types of rocks. We are going to solve a problem about a rock collection.”

• Read the task statement.
• 3 minutes: independent work time
• “Share your thinking with your partner.”
• 2 minutes: partner work time
• Monitor for students who represent their thinking using 10-frames to show 14 and then add 3 more.

• Invite previously identified students to share.
• “How did the representation change when they added three ones? What stayed the same?” (You start with a full 10-frame and four ones, and when you add three more, that 10-frame does not change. This 10-frame changed because now there are four red counters and three yellow counters.)

The purpose of this activity is for students to add a one-digit number to a teen number. All of the totals are within 20. Students are provided 10-frames and two-color counters which they may choose to use to represent the sums. Using 10-frames encourages students to see that the unit of ten stays the same and the ones are combined.

During the activity synthesis, the teacher records how students found the value of the sum of \(17 +2\). It is important that the teacher write the equation the way that students think about the answer to the problem. For example, the equation \(17 + 2 = \boxed{19}\) represents students who show 17 counters and count on as they add two more. The equation \(7 + 2 + 10 = \boxed{19}\) or \(10+7 + 2 = \boxed{19}\) represents students who see that the ten stays the same and they can add the ones to help them find the total.

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

• Read the task statement.
• 5 minutes: independent work time
• 2 minutes: partner discussion
• Monitor for students who find the value of the sum \(17 + 2\) in these ways:
  • \(17 + 2 = \boxed{19}\)
  • \( 7 + 2 + 10 = \boxed{19}\)

• Display each missing number.
• Invite previously identified students to share.
• “How does \(17 + 2 = \boxed{19}\) match _____’s work?” (They put 17 on and then counted 2 more—18, 19—to get the value.)
• “How does \( 7 + 2 + 10 = \boxed{19}\) match _____’s work?” (They added the ones and got 9 and then added 10 to get 19.)

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

• Compare
• Number Puzzles
• Find the Pair
   

• Gather materials from previous centers:
  • Compare, Stage 1
  • Number Puzzles, Stage 1
  • Find the Pair, Stage 2

• 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 first.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice.
• 8 minutes: center work time
• “Choose what you would like to do next.”
• 8 minutes: center work time

• “How do you choose which center will be most helpful for you?”