Lesson 2
Fluency Flip
Warmup: True or False: Sums within 20 (10 minutes)
Narrative
The purpose of this warmup is to elicit strategies and understandings students have for making expressions that are equivalent, but easier to find. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to find missing digits that make equivalent expressions.
Launch
 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
Activity
 Share and record answers and strategies.
 Repeat with each statement.
Student Facing
Decide if each statement is true or false. Be prepared to explain your reasoning.
 \(8 + 5 = 8 + 2 + 5\)
 \(8 + 5 = 8 + 2 + 3\)
 \(8 + 5 = 10 + 3\)
Student Response
Teachers with a valid work email address can click here to register or sign in for free access to Student Response.
Activity Synthesis
 “How can the second statement help you with the last one?”
Activity 1: Heads Up: Make 20 (20 minutes)
Narrative
The purpose of this activity is for students to add or subtract to find unknown addends within 20. Students will find unknown addends when the total is 20. The known addends may encourage students to think about ways to make a ten and to use the sums and differences that they know (MP7).
Advances: Representing, Conversing
Supports accessibility for: SocialEmotional Functioning, Attention
Required Materials
Materials to Copy
 Number Cards 019
Required Preparation

Create a set of cards for each group of 2.
Launch
 Groups of 2
 Give each group a set of cards.
Activity
 “Let’s play another game to find unknown addends.”
 Select a volunteer to be your partner.
 “Partner A will draw a card and hold it on their forehead without looking.”
 Prompt the volunteer to demonstrate.
 “Partner B names a number that you can add to the number on the card to get to 20.”
 Think aloud finding and naming the number.
 “Partner A then names the number they are holding on their head.”
 Prompt the volunteer to find the number.
 “Check your work and write an equation to represent how you found an unknown addend in the turn. Share your equation with your partner. Switch roles and play again.”
 12 minutes: partner work time
 Monitor for students who:
 use place value reasoning or look to make 10
 use known addition or subtraction facts
 make equivalent, but easier sums or differences
Student Facing
 Partner A holds a card on their forehead without looking.
 Partner B names the number that you can add to the number on the card to get 20.
 Partner A says the number on their card.
 Record an equation to represent how you found the unknown addend.
my equations  my partner’s equations 

Student Response
Teachers with a valid work email address can click here to register or sign in for free access to Student Response.
Activity Synthesis
 “Mai thought of trying to make 2 tens. What number needs to be added to 12 to make 2 tens?”
 “What other methods did you use to find the unknown addend?”
 Invite previously identified students to share methods.
 “Pull out the number cards for 0–9, as you will use them in the next activity.”
Activity 2: Number Mix Up (15 minutes)
Narrative
The purpose of this activity is for students to create different expressions that have the same value. The activity encourages students to decompose numbers and to consider how they may create sums that are equivalent but easier to find as a mental strategy (MP7). Students use the number cards 0–9 from the previous activity to help them figure out the missing number in the equations.
Required Materials
Required Preparation
 Each group of 2 needs the digit cards 0–9 from the card set used in the previous activity.
Launch
 Groups of 2
 Give each group a copy of the puzzles.
Activity
 “You are going to use your cards to complete number puzzles. You may only use numbers 0 through 9. You may only use each number one time to make all the equations true.”
 10 minutes: partner work time
Student Response
Teachers with a valid work email address can click here to register or sign in for free access to Student Response.
Advancing Student Thinking
 “Which equations could only be made true using one of your digits?”
 “Which equations have many ways you could make them true?”
Activity Synthesis
 “What did you do when you ended with digits that you could not use to complete a true equation?” (We thought of other numbers that would work with what we had left. We completed the equations that had only 1 unknown first.)
Lesson Synthesis
Lesson Synthesis
“Share your work from the cooldown with your partner. Then we’ll share with the whole class.”
Cooldown: Just the Facts (5 minutes)
CoolDown
Teachers with a valid work email address can click here to register or sign in for free access to CoolDowns.