# Lesson 10

Write Number Riddles

## Warm-up: True or False: Add within 100 (10 minutes)

### Narrative

The purpose of this True or False is to elicit strategies and understandings students have for adding within 100.

### 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 equation.

### Student Facing

Decide if each statement is true or false.

Be prepared to explain your reasoning.

• $$60 = 25 + 45$$

• $$70 = 24 + 46$$

• $$80 = 32 + 37$$

### Activity Synthesis

• “How can you explain your answer without finding the value of the sums on the right side?”

## Activity 1: Write Number Riddles (15 minutes)

### Narrative

The purpose of this activity is for students to write number riddles. Students choose a secret number between 1 and 120, and write four clues that will help their classmates identify the number. As students work, the teacher should review students’ riddles and monitor for groups that may need help writing clues.

Representation: Develop Language and Symbols. Maintain a visible display to record terms and phrases that will be useful in writing Number Riddles such as: number of tens, number of ones, more than, less than.
Supports accessibility for: Memory, Language

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give each group four index cards, a bag or envelope, and access to connecting cubes in towers of 10 and singles.
• “When we solved number riddles, what types of clues did we see?” (number of tens, number of ones, more than, less than, addition)
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Record responses.

### Activity

• “Now you will write a number riddle with your partner. You will write four clues. One clue should be an addition expression that will be the last clue. Write each clue on an index card and make sure that your number fits all the clues. Fold the card with the addition expression in half.”
• 10 minutes: partner work time
• “What is your secret number?”
• “What number(s) is your secret number greater than? Less than?”
• “What do you know about the tens and ones in your secret number?”
• “What numbers can you add (subtract) to get this number?”

### Student Facing

Our secret number: ____________
Our 4 clues:

• Write each clue on an index card.
• Make sure the last clue is an addition expression.
• Fold that clue in half.

### Advancing Student Thinking

If students write fewer than three clues, consider asking:

• “What do you know about your secret number?”
• “How can you write a clue using ‘greater than’ or ‘less than’ or __ tens or ones?”

### Activity Synthesis

• “Put your clues in an envelope and write your names on the envelope.”

## Activity 2: Solve Our Number Riddles (20 minutes)

### Narrative

The purpose of this activity is for students to apply place value reasoning to solve number riddles written by their classmates. When students solve the number riddles they use their understanding of the number sequence and place value (MP7).

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

### Required Materials

Materials to Gather

### Required Preparation

• Each group of 2 needs to begin with a riddle envelope from the previous activity.

### Launch

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

### Activity

• “Now you are going to solve your classmates’ riddles. Use your workbook page as a place to record your ideas as you solve. When you finish solving a riddle, put it back in the envelope and look for another group who is ready to trade riddles with you.”
• 15 minutes: partner work time

### Student Facing

Record your ideas as you solve each number riddle.

### Activity Synthesis

• “Were there any number riddles that were challenging to solve? Why were they more challenging than the other riddles?”

## Lesson Synthesis

### Lesson Synthesis

“Share your work from the cool-down with your partner.”

Invite students to share with the whole class.