standard_description: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
problem_activity: Narrative
The purpose of this activity is for students to play a game that enables them to practice using strategies and algorithms to subtract within 1,000. Students decide whether they will try to make the smallest or greatest difference, then spin a paper clip on a spinner to generate two three-digit numbers. Students use their choice of strategy or algorithm to subtract the numbers.
When students use place value to create a pair of numbers with a specific type of difference, they are looking for and making use of structure (MP7).
Required Materials
Materials to Gather
Paper clips
Pencils
Materials to Copy
Greatest Difference, Smallest Difference
Required Preparation
Each group of 2 will need a paper clip.
Launch
Groups of 2
Give each group 1 copy of Greatest Difference, Smallest Difference.
“Take a minute and read the directions to the game with your partner.”
1 minute: partner work time
Play one round of the game against the class to illustrate how the game should be played.
“Are there any questions about the game?”
Answer any questions students have about the game.
Activity
“Now, take some time and play the game with your partner.”
7–10 minutes: partner work time
Student Facing
Decide with your partner whether you will try to make the greatest difference or smallest difference.
Take turns spinning and recording a digit in the hundreds, tens, or ones place. Continue until your numbers are complete.
Find the difference.
Compare your values.
Write a comparison using >, <, or =.
Play again.
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Student Response
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Activity Synthesis
Display: 601 and 398
“If these were the numbers you made, how would you find the difference and why?” (Sample responses: I would count up because 398 is so close to 400. I would use an algorithm because I know that if I follow the steps it would work every time.)


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