Lesson 18
Equations with Unknowns
Warmup: Notice and Wonder: Equations with an Unknown (10 minutes)
Narrative
Launch
 Groups of 2
 Display the image.
 “What do you notice? What do you wonder?”
 1 minute: quiet think time
Activity
 “Discuss your thinking with your partner.”
 1 minute: partner discussion
 Share and record responses.
Student Facing
What do you notice?
What do you wonder?
\(4 + \boxed{\phantom{\frac{aaai}{aaai}}} = 10\)
Student Response
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Activity Synthesis
 “How does the equation with the unknown value match the picture?” (There are 4 basketballs in the open bag and there are some more things in the other bag but we don't know how many. There must be 10 altogether.)
Activity 1: Match Stories and Equations (20 minutes)
Narrative
The purpose of this activity is for students to match story problems to equations with a symbol for the unknown (MP2). Each equation is written to match the way the numbers are presented in the story problem. Problem G has more than one equation, which prompts students to discuss the relationship between addition and subtraction (MP7). During the synthesis, students discuss how an equation with a symbol for the unknown matches a Take From, Result Unknown story problem.
Supports accessibility for: Language,Memory
Required Materials
Materials to Copy
 Story Problem Cards Grade 1
 Equation Cards Grade 1
Required Preparation
 Create a set of Story Problem Cards and Equation Cards for each group of 2.
Launch
 Groups of 2
 Give each group a set of both cards.
Activity
 “You have two sets of cards. One set of cards has the story problems we used in the last lesson. The other set of cards has equations with unknown values.”
 “Work with your partner to match the story problems to the equations. One story has more than one equation. Be sure you can explain how you know they match.”
 10 minutes: partner work time
Student Response
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Activity Synthesis
 “Which equation matches Card C? How do you know?” (\(9  6 = \boxed{\phantom{3}}\). 9 represents how many students were sliding. 6 represents how many students leave so that is \(9  6\). The box represents how many are left, which is the answer to the problem.)
 Repeat for problems F and H.
 Display equation cards 6 and 8.
 "What do you notice about these equations?" (They both have a total of 9 and one part is 4. The other part is the unknown. They both match problem G.)
 “How does each of these equations match the story problem?” (There are 9 students jumping Double Dutch and 4 students jumping on their own. I need to find the difference, so I can subtract \(9  4\) to find the answer or I can say that \(9 = 4 + \boxed{\phantom{5}}\). 9 equals 4 plus some more students.)
Activity 2: Which Equation? (15 minutes)
Narrative
Advances: Reading, Representing
Required Materials
Materials to Gather
Launch
 Groups of 2
 Give students access to connecting cubes or twocolor counters.
 “We are going to look at one more story and two equations that match. This story is about students playing the game called bingo.”
Activity
 Read the task statement.
 5 minutes: independent work time
 4 minutes: partner discussion
 Monitor for students who create a clear drawing and can use it to explain how each equation matches the story.
Student Facing
9 students are playing bingo.
3 students are using blue chips to cover their boards.
The other students are using yellow chips.
How many students are using yellow chips?
Explain how each equation matches the story problem.
Show your thinking using drawings, numbers, or words.

Clare wrote \(3 + \boxed{\phantom{6}} = 9\)

Jada wrote \(9  3 = \boxed{\phantom{6}}\)
Student Response
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Activity Synthesis
 Invite previously identified students to share.
 “How do the equations relate to each other?” (The second equation can be used to find the missing number in the first equation. The number that goes in the box is the same.)
Lesson Synthesis
Lesson Synthesis
“Today, we saw that for some story problems, there are addition and subtraction equations that can match the problem. Which kind of equation do you prefer to write? Why?"
Cooldown: Lin’s Bingo Chips (5 minutes)
CoolDown
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