Lesson objective: Practice using part/part/whole diagrams to model math situations.

This lesson helps to build procedural skill with whole number addition and subtraction. Part/part/whole diagrams are used here because they highlight the relationship between the parts and the whole in problem situations. This work develops students' understanding that we can find unknown values in addition or subtraction situations using the relationship between addition and subtraction.

Students engage in Mathematical Practice 1 as they make sense of problems and persevere in solving them, which is central to the work in this task. Students will need to determine the meaning of the problem and consider entry points that will lead to a solution. Students may rely on pictures or models to help conceptualize the problem. They understand that there may be multiple ways to find the solution. As they work through the task, students should be asking themselves, “Does this make sense?”

**Key vocabulary:**

- part/part/whole diagram
- part
- whole

**Special materials needed:**

- place value tools for concrete learners