# Lesson 16

Our Market’s Inventory (optional)

### Lesson Purpose

The purpose of this lesson is for students to apply strategies for adding and subtracting within 100 within the context of a store.

### Lesson Narrative

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 learned how to add and subtract within 100. In this lesson, students role-play buying and selling items in a store. Students are responsible for selling 3 types of goods and keeping 100 items in stock for sale.

In the first activity students adhere to certain constraints and choose what they want to sell and how much they want to sell. When students make decisions and choices and adhere to constraints, they model with mathematics (MP4). They set up their inventory sheet to keep track of their sales. In the second activity they take turns buying and selling. Sellers keep track of their inventory after each sale and at the end consider what they need to restock. When students analyze numerical information and interpret results, they model with mathematics (MP4).

An optional third activity gives students an opportunity to present a sales report.

• Representation
• MLR8

### Required Materials

Materials to Gather

Building Towards

### Lesson Timeline

 Warm-up 10 min Activity 1 10 min Activity 2 20 min Activity 3 15 min Lesson Synthesis 10 min

### Teacher Reflection Questions

If you were to teach this lesson over again, what activity would you redo? How would your proposed changes support student learning?

### Suggested Centers

• Target Numbers (1–5), Stage 5: Subtract Two-digit Numbers (Addressing)
• Math Stories (K–2), Stage 5: Tape Diagrams (Addressing)