# Lesson 5

Put Together and Take Apart Story Problems

## Warm-up: True or False: More or Less (10 minutes)

### Narrative

The purpose of this True or False is to elicit strategies and understandings students have for place value and the operations of addition and subtraction (MP7). Students may use these understandings to reason about whether each equation is true or false without finding the value of the 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.

• $$57 + 20 = 59$$
• $$66 - 4 = 62$$
• $$17 + 76 = 59$$

### Activity Synthesis

• “How can you explain your answer without finding the value of the expression?”

## Activity 1: At the Planetarium (20 minutes)

### Narrative

The purpose of this activity is for students to make sense of and solve Put Together/Take Apart, Addend Unknown story problems (MP2). In the synthesis, students discuss different methods used to solve these problems, including using addition and subtraction.

The teacher may want to incorporate movement into this activity by writing each problem on a piece of chart paper and placing each one in a different location around the classroom. Students can solve the problem at one location, discuss the problem with their partner, then move on to a new problem at a new location.

Engagement: Provide Access by Recruiting Interest. Provide choice. Invite students to decide which problem to start with.
Supports accessibility for: Attention, Social-Emotional Functioning

### Launch

• Groups of 2
• Give each group access to connecting cubes in towers of 10 and singles.
• Display the image in the student book.
• “What do you notice in this picture? What do you wonder?” (There are bright colors. This looks like stars in the sky. Why is there red in the sky? Where is this?)
• “This is a picture of something called the Helix Nebula. It is one of many interesting things that can be seen in our sky. People who are interested in learning more about stars, planets, or anything else that is found in the sky, can visit a planetarium to learn all about these things. We are going to solve some problems about a field trip to the planetarium.”

### Activity

• 8 minutes: independent work time
• 4 minutes: partner discussion
• Monitor for students who solve the problem about bright and dim stars with addition and for students who solve the same problem with subtraction.

### Student Facing

Solve each problem.
Show your thinking using drawings, numbers, or words.

1. There are 7 first graders and some second graders at the planetarium.
There are 18 students at the planetarium.
How many second graders are at the planetarium?

2. When the show started, 18 stars lit up in the sky.
13 stars were bright.
Some of the stars were dim.
How many stars were dim?

3. Together, Diego and Tyler saw 15 shooting stars during the show.
Diego saw 6 shooting stars. Tyler saw the rest.
How many shooting stars did Tyler see?

4. In the gift shop, Elena bought 12 star stickers.
She also bought some planet stickers.
Elena bought 20 stickers.
How many planet stickers did she buy?

### Student Response

If students attempt to solve each problem by adding the known quantities, consider asking:

• “What is the story problem about? What do you know? What do you need to figure out?”
• “What did you do to solve the problem?”
• “What does your answer mean in the story? Does it make sense?”

### Activity Synthesis

• Display $$15 - 6 = \boxed{\phantom{3}}$$ and $$6 + \boxed{\phantom{3}} = 15$$
• “How do both of these equations help you find the number of shooting stars Tyler saw?”
• Invite previously identified students to share. As needed, ask students to connect the numbers they use to the story problem.
• “How are these methods the same? How are they different?” (They both find the same number of dim stars. Both show that there’s some bright stars, some dim stars, and a total number. One way uses addition to count on from the number of bright stars. One uses subtraction to take away the number of bright stars from the total.)

## Activity 2: Which Equations Match? (15 minutes)

### Narrative

The purpose of this activity is for students to identify different equations that can be used to represent the same problem. Students explain why each equation does or does not represent the story. This helps students understand that Put Together/Take Apart story problems can be represented and solved with either addition or subtraction when an addend is unknown (MP2).

MLR8 Discussion Supports. Students should take turns finding a match and explaining their reasoning to their partner. Display the following sentence frames for all to see: “I noticed _____, so I matched . . . .” Encourage students to challenge each other when they disagree.

### Launch

• Groups of 2
• Give each group access to connecting cubes in towers of 10 and singles.

### Activity

• 10 minutes: partner work time

### Student Facing

Circle 2 equations that can be used to solve each problem.
Be ready to explain how the equations represent the story and why the other equation doesn’t.

1. Noah painted 9 white stars.
He also painted some yellow stars.
Noah painted 17 stars all together.
How many yellow stars did Noah paint?

1. $$17 - 9 = \boxed{\phantom{3}}$$
2. $$9 + 17 = \boxed{\phantom{3}}$$
3. $$9 + \boxed{\phantom{3}} = 17$$
2. Kiran saw 16 objects in the sky.
11 of the objects were stars.
The rest of the objects were planets.
How many of the objects were planets?

1. $$16 + 11 = \boxed{\phantom{3}}$$
2. $$11 + \boxed{\phantom{3}} = 16$$
3. $$16 - 11 = \boxed{\phantom{3}}$$

If you have time: Solve each problem using both equations.

### Activity Synthesis

• For each problem:
• Invite students to share how each equation they chose represents the problem.
• Invite students to share why one of the equations does not represent the problem.

## Lesson Synthesis

### Lesson Synthesis

“Today we solved story problems where there was a total number of objects and two different parts. We knew the total number and the number of one of the parts. We used addition and subtraction to represent the problem and find the unknown number.”

“Why can you use either addition or subtraction to find the unknown number?” (You can use addition because you know one part, so you can think of what to add to get to the total. It’s like when we use addition to find the answer to subtraction. You can use subtraction because if you take away the number of one of the parts, the unknown number is what is left.)

“When we matched equations to the story problems, what did you notice about the equations that did not match? Can you add the numbers in the problem anyway you want?” (You can’t just add the numbers in the problem. You have to make sure they match what the story is about.)