Lesson 20
A Trip to the Zoo
Warmup: Number Talk: Using $10 + \boxed{\phantom{4}}$ (10 minutes)
Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for adding within 20.
Students may have many ideas for adding these numbers. In the synthesis, students discuss what they notice about the first two expressions. Students may notice that the expressions are equal and that one expression might help them with the other.
Launch
 Display one expression.
 “Give me a signal when you have an answer and can explain how you got it.”
 1 minute: quiet think time
Activity
 Record answers and strategy.
 Keep expressions and work displayed.
 Repeat with each expression.
Student Facing
Find the value of each expression mentally.
 \(8 + 2 + 4\)
 \(8 + 6\)
 \(7 + 3 + 6\)
 \(7 + 9\)
Student Response
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Activity Synthesis
 “What do you notice about the first two expressions?” (They are both 14. If 6 was broken into 2 and 4, it would be the same expression.)
Activity 1: How Many Reptiles? (15 minutes)
Narrative
The purpose of this activity is for students to discuss different ways to solve a threeaddend story problem in which none of the addends can be combined to make 10 without being decomposed. Students solve the problem in a way that makes sense to them. Some students may build each number separately on the 10frames and see both are filled. Some students may manipulate the numbers and think \(8 + 7 + 5 = 8 + 2 + 5 + 5\). Different methods for solving are highlighted in the synthesis. It is important that the teacher represents student thinking, so that these methods are visible to all.
When students make sense of the story problems and connect the quantities in the story to an equation, they reason abstractly and quantitatively (MP2).
Advances: Reading, Representing
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to double 10frames and connecting cubes or twocolor counters.
Activity
 Read the task statement.
 4 minutes: independent work time
 2 minutes: partner discussion
 Monitor for students who:
 place 8, 7, and 5 counters on the 10frames and see that they are both full
 count on
 represent the problem as \(8 + 2 + 5 + 5\)
 use a known sum like \(8 + 8\) and then add 4 more.
Student Facing
Jada went to the zoo with her family.
They went to the reptile exhibit and saw 8 snakes, 7 iguanas, and 5 frogs.
How many reptiles did Jada's family see?
Show your thinking using drawings, numbers, or words.
Student Response
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Activity Synthesis
 Invite previously identified students to share.
 “What did they do to find the sum?”
 Record each method with an equation.
Activity 2: Zoo Exhibits (20 minutes)
Narrative
In this activity students solve threeaddend story problems within 20. Students use methods and representations that make sense to them. When students connect the quantities in the story to an equation, they reason abstractly and quantitatively (MP2). They think strategically and may either choose to use a double 10frame or decompose and compose the numbers in a way that helps them see the sum as 10 and some ones (MP1, MP5).
Supports accessibility for: Organization, Attention
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to double 10frames and connecting cubes or twocolor counters.
 “We are going to solve some problems using the different methods we’ve been working on.”
Activity
 Read the task statement.
 6–8 minutes: independent work time
 4 minutes: partner discussion
Student Facing

In the bird exhibit, Jada saw 3 herons, 6 hawks, and 7 hummingbirds.
How many birds did Jada see?
Show your thinking using drawings, numbers, or words.  Next Jada went to the large cat exhibit.
There were 8 lions, 4 tigers, and 3 cheetahs.
How many large cats were there?
Show your thinking using drawings, numbers, or words.  Finally, Jada went to the petting zoo.
She petted 8 goats, 7 sheep, and 4 pigs.
How many animals did Jada pet?
Show your thinking using drawings, numbers, or words.
Student Response
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Activity Synthesis
 Invite students to share their method for each problem.
 Record each method with an equation.
Lesson Synthesis
Lesson Synthesis
“In this section, we worked on different ways to add within 20. What are you most proud of? What do you still need to practice?”
Cooldown: A Visit with the Primates (5 minutes)
CoolDown
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Student Section Summary
Student Facing
We saw that making a ten could help when we add 3 numbers together.
\(4 + 8 + 6 = 10 + 8 = 18\)
We saw that making a ten could also help when we add 2 numbers together.
\(4 + 8 = 4 + 6 + 2 = 10 + 2 = 12\)