The purpose of this activity is for students to compare two book fair scenarios in which there is a different base price of a book for the fundraiser. Students notice that when you increase the price of a book by a large amount of money, you make more profit per book, but you may also sell fewer books. On the other hand, if you increase the price by a smaller amount of money, you have to sell more books to make the same profit.

• “¿Cuál es un precio con ganancia razonable?” // “What is a reasonable mark-up price?” (I think 2 is reasonable because that would keep the price lower and you would sell more books. I think 5 is reasonable because then you would make more money from each book.)
• “¿Qué deben considerar al decidir un precio con ganancia?” // “What do you need to consider when deciding a mark-up price?” (You have to mark it up enough to make a profit, but not so much that it's too expensive for people to buy.)

The purpose of this activity is for students to plan a school book fair. They choose the types of books to order and the cost for each type of book. They also estimate how many people might come to the book fair and how much money the school might raise from the book fair.

Students will have to make many assumptions in this activity: how many people are coming to the book fair, how many books each person will buy, and how much to add to the price of the book. When students consider assumptions about information not given in a situation, they model with mathematics (MP4).

• Invite students to share their book fair plans.
• Invite students to share their assumptions.
• “¿Por qué hicieron estas suposiciones?” // “Why did you make these assumptions?” (There are 600 students, so I thought that maybe only half would come since that is usually what happens. Since the school wants to make a profit, but also make the books affordable, the mark-up price is only one more dollar than the list price.)