# Lesson 7

Center Day 1 (optional)

## Warm-up: True or False: Compare to 100 (10 minutes)

### Narrative

The purpose of this True or False is to elicit strategies and understanding students have for comparing numbers and expressions to 100. Students have opportunities to share what they understand about 100 based on place value and by reasoning about the position of 100 on the number line. These ideas will also be helpful in future lessons when students place numbers within 1,000 on the number line and compare three-digit numbers based on place value.

### 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 strategy.
• Repeat with each statement.

### Student Facing

Decide if each statement is true or false. Be prepared to explain your reasoning.

• $$100 > 99$$
• $$100 < 99 + 1$$
• $$98 + 3 > 100$$
• $$50 + 50 + 50 > 100$$

### Activity Synthesis

• “How did you know that $$100 < 99 + 1$$ was false?” (99 plus 1 more is 100. When we count, 100 is the next number. They are equal.)

## Activity 1: Introduce Mystery Number, Three-digit Numbers (15 minutes)

### Narrative

The purpose of this activity is for students to learn stage 2 of the Mystery Number center. Students pick 3 cards and make a mystery three-digit number. Students give clues based on the sentence starters and their partner tries to guess their number. Students should remove cards that show 10 from their deck. When they give clues and guess the number, students demonstrate understanding of the base-ten system, both the  meaning of each digit in a number and the order of the numbers (MP7).

### Required Materials

Materials to Gather

Materials to Copy

• Mystery Number Stage 2 Directions

### Launch

• Groups of 2
• Give each group a set of number cards and directions.
• “We are going to learn a new center called Mystery Number that you might have played in first grade. You will pick 3 cards and make a mystery three-digit number. Then you will give your partner clues and they will try to guess your mystery number.”
• “Read the directions with your partner to see if you have any questions.”
• Answer any questions or play a round against the class to demonstrate the center.

### Activity

• 15 minutes: partner work time
• Monitor for clues to share during the synthesis.

### Activity Synthesis

• “What types of clues were particularly helpful to you when you were trying to guess your partner’s number?”

## Activity 2: Centers: Choice Time (20 minutes)

### Narrative

The purpose of this activity is for students to choose from activities that focus on addition or subtraction. Students choose from any stage of previously introduced centers.

• Jump the Line
• Mystery Number
• Number Puzzles

### Required Materials

Materials to Gather

### Required Preparation

Gather materials from:

• Jump the Line, Stage 1
• Mystery Number, Stage 2
• Number Puzzles, Stages 24

### Launch

• “Now you will choose from centers we have already learned. One of the choices is to continue with Mystery Number.”
• Display the center choices in the student book.
• “Think about what you would like to do first.”
• 30 seconds: quiet think time

### Activity

• Invite students to work at the center of their choice.
• 10 minutes: center work time
• “Choose what you would like to do next.”
• 10 minutes: center work time

Choose a center.

Jump the Line

Mystery Number

Number Puzzles

### Activity Synthesis

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

## Lesson Synthesis

### Lesson Synthesis

“Today we described and guessed mystery numbers and practiced adding and subtracting. Tell your partner what you needed to remember about place value when you played today's centers.” (You have to know the 3 digits represent hundreds, tens and ones. You have to know that 4 tens really means 40, not 4.)