Lesson 15

The purpose of this lesson is for students to generate their own addition and subtraction stories, and use the number line as a tool to write and solve story problems.

This lesson is optional because it does not address any new mathematical content standards. This lesson does provide students with an opportunity to apply precursor skills of mathematical modeling.

In previous lessons, students represented addition and subtraction on the number line and considered different methods based on the numbers being added and subtracted.

In this lesson, students apply previous understandings of the methods and representations for addition and subtraction problems within 100 to write and solve their own real-world problems. Students are encouraged to use the number line to represent the ages and solve problems. In the first activity, they become familiar with the context by solving problems about ages using any method that makes sense to them. In the second activity, they write their own problems about the ages of people they know, represent the problems, and solve them.

In this lesson, when students decide what quantities are important in a real-world situation, use these quantities to develop their own story problems, and choose math that matches a simplified situation, they build the precursor skills they need to model with mathematics (MP4).

• Create a number line from 0–100, marking intervals of 5, to display during the synthesis.

Students shared their thinking multiple times in this lesson. What have you noticed about the language students use? What support can you offer to students who struggle to communicate their ideas orally?