standard_description: Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.
problem_activity: Narrative
The purpose of this activity is for students to use their understanding of place value to determine the number described in a riddle. Students then write the number of hundreds, tens, and ones, and represent the value as a three-digit number.
MLR8 Discussion Supports.
Display sentence frames to support partner discussion about each number written on the table: “I agree because . . .” or “I disagree because . . . .”
Advances: Conversing
Engagement: Provide Access by Recruiting Interest.
Provide choice. Invite students to decide the order in which they complete the work. They can start with any of the riddles, as long as they complete all of them.
Supports accessibility for: Attention, Social-Emotional Functioning
Required Materials
Materials to Gather
Base-ten blocks
Launch
Groups of 2
Give students access to base-ten blocks.
“I have 4 hundreds, 3 ones, and 2 tens.”
“Which of these shows the total value written as a three-digit number? Explain how you know.”
Display 432, 234, 423.
30 seconds: quiet think time
1 minute: partner discussion
Share responses.
Activity
“You are going to solve number riddles using base-ten blocks.”
As needed, demonstrate the task with a student.
“Take turns reading the clues, while your partner uses blocks to make the number.”
“Make sure you agree before adding each number to the table.”
10 minutes: partner work time
If students finish early, ask them to write their own riddles and trade them with other groups to solve.
Monitor for students who recognize they need a zero when writing the three-digit number in places where there were no tens or no ones.
Student Facing
Solve each riddle and write the three-digit number. Use the table to help you organize the digits.
| riddle | hundreds | tens | ones | three-digit number |
|--------|----------|------|------|--------------------|
|   1    |          |      |      |                    |
|   2    |          |      |      |                    |
|   3    |          |      |      |                    |
|   4    |          |      |      |                    |
|   5    |          |      |      |                    |
|   6    |          |      |      |                    |
I have 2 ones, 7 tens, and 6 hundreds.
I have 3 ones, 5 tens, and 2 hundreds.
I have 7 hundreds, 5 ones, and 3 tens.
I have 5 hundreds, no tens, and 9 ones.
I have 4 ones, 6 tens, and 3 hundreds.
I have 8 tens, 1 hundred, and no ones.
Student Response
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Activity Synthesis
Invite previously selected students to share what they noticed when writing 509 and 180.
As needed, write 81, 801, and 810 and ask, “What is the difference between 81, 801, and 810?”


aligns: no