The purpose of this activity is for students to choose a strategy or an algorithm to subtract within 1,000. Students should attend to the details of numbers in the problems that could indicate whether a particular strategy or algorithm is most useful. The important thing is that students choose an algorithm or another strategy that they can use efficiently and accurately for the given problem. As students choose strategies to find the values of each expression, they look for common structure and observe regularity in repeated reasoning (MP7, MP8).

• Invite 4 or 5 students to share a strategy or an algorithm they saw.
• “What strategies or algorithms do you want to practice more?”

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 least or greatest difference, then they spin a paper clip on a spinner to generate 2 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).

• Display: 601 and 398
• “If these were the numbers you made, how would you find the difference and why?” (I would count up because 398 is so close to 400. I would use an algorithm because I know that if I followed the steps, it would work every time.)