Lesson objective: Understand that number line diagrams can be used to model addition and subtraction of whole numbers that are not lengths.

Students bring prior knowledge of adding and subtracting lengths using a number line from 2.MD.B.5. This prior knowledge is extended to operations with all whole numbers as students use number lines to model many types of addition and subtraction problems. A conceptual challenge students may encounter is understanding the relationship between a quantity of objects and a linear representation on a number line.

The concept is developed through work with number line diagrams, which allow students to visualize the proportions between numbers, as well as part-whole relationships between numbers.

This work helps students deepen their understanding of equivalence because will also use the number line to identify the relationships between two quantities (greater than, less than, or equal to) and use that relationship to add or subtract.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they look for number patterns and relationships on the number line to develop computational strategies.

**Key vocabulary:**

- number line diagram

**Special materials needed:**

- blank number lines (optional)