The purpose of this activity is for students to decide on the inventory for items sold in a store of their choice. They must keep three different items in stock and use their understanding of adding and subtracting within 100 to make sure they have a total of 100 items in their store. They will use their completed inventory sheet in the next activity.

• “What are some ways we can prove that we have exactly 100 items?“ (Add the three numbers and get 100. Subtract two numbers from 100 and get the last number. Add two numbers and then subtract the result from 100 to get the third number.)

The purpose of this activity is for students to role play buying and selling items at one another’s stores. Students roll a number cube and use the results to decide how much of each item they buy in the store. Students use their understanding of adding and subtracting within 100 to keep track of how many of each item is available using their inventory sheet. When students model a real-world situation with a representation, such as a drawing or an equation, they model with mathematics (MP4).

• Invite previously selected students to share.
• “How did you decide how to use rolls strategically, based on what was in the store’s inventory?” (If there were more items, I used a two-digit number. I had to think about which digit goes first.)
• “Did anyone run low on an item? Did anyone run out of an item? What did you tell your buyer?”

The purpose of this activity is for students to add and subtract within 100. They use their inventory sheet to record their total sales, their ending inventory, and the number of items they need to restock for the next day. They use their understanding of the relationship between addition and subtraction to observe that the number of items subtracted (total sales) is the same as the number of items that need to be added to get back to the starting inventory. When students consider the implications of their model, they model with mathematics (MP4).

• Invite previously identified students to share their sales reports.
• “How did you figure out how many of each item needed to be restocked?” (We’re replacing the exact amount that was sold. If we add the restock amount and the number of items left, we get the original starting amount.)