The purpose of this activity is for students to solve word problems that involve adding or subtracting numbers within 1,000, using approaches with which they are familiar from earlier grades. The goal is to elicit and highlight strategies that rely on place-value understanding, in preparation for upcoming work on addition and subtraction algorithms, which also rely on place value.

Monitor for and select students, with the following approaches for solving the last problem about the Eiffel Tower (AYE-fuhl TAOW-ur), to share in the Activity Synthesis:

• Start at 327 and count on by place to 674, using a number line or a series of equations.
• Start at 674 and count back to 327, using a number line or a series of equations.
• Subtract 327 from 674 by taking away hundreds from hundreds, tens from tens, and ones from ones, and decomposing a ten for more ones, using base-ten blocks or a base-ten drawing.

The approaches are sequenced from those based on counting to those that involve explicitly decomposing units. This helps students connect the different ways they use place-value reasoning, and make sense of strategies and recording methods that are increasingly similar to the algorithms students will see in later lessons. Aim to elicit both key mathematical ideas and a variety of student voices, especially students who haven't shared recently. As students interpret quantities in context, reason about ways to represent them, and consider the solutions in terms of the situation, they practice reasoning quantitatively and abstractly (MP2).

For an example of each approach, look at the Student Responses for the last problem.

• Invite previously selected students to share in the given order. Record or display their work for all to see.
• Connect students’ approaches by asking:
  • “¿En qué se parecen estas formas de resolver el problema?” // “How are these ways of solving the problem the same?” (Both show 674 and 327. Both show thinking about place value.)
  • “¿En qué son diferentes?” // “How are they different?” (Some ways show counting on or back to a hundred or a ten. Another way shows drawing hundreds, tens, and ones, and decomposing a ten.)
• If no students mention using place value to find the values of sums or differences, connect their approaches to the learning goal by asking:
  • “¿Cómo usaron en esta actividad lo que saben sobre el valor posicional para encontrar las sumas y las diferencias?” // “How did you use what you know about place value to find the sums and differences in this activity?”

The purpose of this activity is for students to reflect on the strategies they used in the first activity. This is an opportunity to check in with students about the strategies from grade 2 that they are comfortable using and those they find more challenging.

• Invite 2 or 3 students to share their journal responses with the class.