# Lesson 17

Center Day 3 (optional)

## Warm-up: Number Talk: Simplify It (10 minutes)

### Narrative

The purpose of this Number Talk is to elicit strategies and understandings students have for adjusting the numbers in an expression to make it easier to find the value. These understandings help students develop fluency.

### 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.

- \(34 - 9\)
- \(434 - 99\)
- \(367 - 98\)
- \(635 - 298\)

### Student Response

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### Activity Synthesis

- “When you change one number in an expression to make it easier, how do you remember how to adjust any other numbers in the expression?”

## Activity 1: Introduce Target Numbers, Add Hundreds, Tens, or Ones (15 minutes)

### Narrative

The purpose of this activity is for students to learn stage 6 of the Target Numbers center. Students add hundreds, tens, and ones to get as close to 1,000 as possible.

### Required Materials

### Required Preparation

Each group of 2 needs 3 number cubes.

### Launch

- Groups of 2
- Give each group number cubes and two recording sheets.
- “We are going to learn a new way to play the Target Numbers center.”
- “In this version, you add hundreds, tens, and ones to get as close to 1,000 as possible.”
- “Take a minute to read the directions with your partner.”
- Answer any questions or play a round with the class as needed.
- “Play this new version of Target Numbers with your partner.”

### Activity

- 10 minutes: partner work time

### Activity Synthesis

- “How did you decide which numbers you rolled would be hundreds, tens, or ones?”

## Activity 2: More Target Numbers and Choice Time (25 minutes)

### Narrative

The purpose of this activity is for students to learn stage 7 of the Target Numbers center. Students subtract hundreds, tens, and ones to get as close to 0 as possible. Then, students choose from any stage of previously introduced centers.

- Target Numbers
- Five in a Row
- How Close?

### Required Materials

Materials to Gather

### Required Preparation

- Each group of 2 students needs 3 number cubes.
- Gather materials from:
- Target Numbers, Stage 6
- Five in a Row, Stages 7 and 8
- How Close, Stage 4

### Launch

- Groups of 2
- Give each group number cubes and two recording sheets.
- “We are going to learn another new way to play the Target Numbers center. In this version, you subtract hundreds, tens, and ones to get as close to 0 as possible.”
- “Take a minute to read the directions with your partner.”
- Answer any questions.
- “Play this new version of Target Numbers with your partner.”

### Activity

- 10 minutes: partner work time
- “Now you can choose another center. You can also continue playing Target Numbers.”
- Display the center choices in the student book.
- Invite students to work at the center of their choice.
- 10 minutes: center work time
- If time, invite students to choose another center.

### Student Facing

Choose a center.

Target Numbers

Five in a Row: Addition and Subtraction

How Close?

### Activity Synthesis

- “What did you like about the activities you worked on today?”

## Lesson Synthesis

### Lesson Synthesis

“How did you and your partner work together during centers? What went well? What can we continue to work on?”