The purpose of this activity is for students to compare two methods to record a newly composed ten or hundred when using the same algorithm. The first method, which students saw in a previous lesson, records the newly composed ten or hundred as ““10” or “100,” respectively, at the top of the problem. The second method records the newly composed ten or hundred as a single digit of 1 at the top of the tens or hundreds column, respectively. It is important that students understand an additional 1 in the tens column represents a newly composed ten, and an additional 1 in the hundreds column represents a newly composed hundred. Students interpret the work and thinking shown in the different methods, and discuss the similarities and differences (MP3).

• Display student's work for each problem.
• Consider asking:
  • “Why did we need to put a 1 in the tens (or hundreds) column?”
  • “What does the 1 in the tens (or hundreds) column represent?”
• ”A newly composed unit can be recorded with a single digit. What does the single digit represent?” (If it’s in the tens place, it stands for 10. If it’s in the hundreds place, it stands for 100.)
• ”How does place value help us remember what the additional ones represent?” (If the 1 is in the tens column, it represents 10. If it is in the hundreds column, it represents 100.)

The purpose of this activity is for students to choose an algorithm, or other strategy, to add within 1,000. Students should attend to the details of the numbers in the problems, which could indicate whether a particular strategy or algorithm is most useful. The important thing is that students choose an algorithm or a strategy that they can use efficiently and accurately for the given problem.

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