# Lesson 22

Center Day 4

## Warm-up: True or False: Tens and Ones (10 minutes)

### Narrative

The purpose of this True or False is to elicit insights students have about numbers being represented in different ways. The reasoning students do here deepens their understanding of how numbers can be composed and decomposed in different ways using tens and ones.

### 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.

- \(92 = 90 + 2\)
- \(90 + 2 > 80 + 12\)
- \(20 + 13 < 30 + 13\)

### Student Response

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### Activity Synthesis

- “How can you determine whether each is true or false without finding the value of each side?”
- If needed, ask “How can you use what you know about tens and ones to help you know if it is true or false?” (I can compare the number of tens first, then compare ones.)

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

### Narrative

The purpose of this activity is for students to learn a new center called Mystery Number. Each student has a mystery number. They give clues to their partner based on sentence stems. After each clue, the partner guesses the mystery number. Players earn points based on how many clues they need to identify the mystery number. The player with the lowest score after five rounds wins.

### Required Materials

### Launch

- Groups of 2
- Give each group a set of cards and directions.
- “We are going to learn a new center called Mystery Number.”
- “On your turn, you will choose two number cards and make a two-digit number. Then use one of the sentence starters to give a clue to your partner. Your partner can guess your number. If they don’t guess the correct number, give them another clue. Continue until they guess your number. The person guessing gets one point for every clue they get to help them guess. Continue playing for five rounds. The person with the lowest score wins.”

### Activity

- 10 minutes: partner work time

### Activity Synthesis

- “Which clues made your partner’s number easiest to guess?”

## Activity 2: Center: Choice Time (25 minutes)

### Narrative

The purpose of this activity is for students to choose from activities that offer practice working with two-digit numbers. Students choose from previously introduced centers.

- Mystery Number
- Get Your Numbers in Order
- Greatest of Them All

### Required Materials

Materials to Gather

### Required Preparation

- Gather materials from previous centers:
- Mystery Number, Stage 1
- Get Your Numbers in Order, Stage 1
- Greatest of Them All, Stage 1

### Launch

- Groups of 2
- “We are going to choose from centers we have already learned.”
- Display the student page.
- “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

### Student Facing

Choose a center.

Mystery Number

Get Your Numbers in Order

Greatest of Them All

### Activity Synthesis

- “How were the two centers you worked on the same? How were they different?”