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 (MP4).

In previous lessons, students learned how to add and subtract within 100. In this lesson, students use these skills to model a real-world situation. Students role play buying and selling items in a store. They are given constraints and choose what they want to sell and how much they want to sell. They keep track of their sales and consider what is needed in order to restock their store.