Lesson 26

The purpose of this warm-up is to introduce the idea of a book sale, which will be useful when students work with this context in a later activity. While students may notice and wonder many things about these images, the range of and prices and types of books are the important discussion points.

• Groups of 2
• Display the image.
• “¿Qué observan? ¿Qué se preguntan?” // “What do you notice? What do you wonder?”
• 1 minute: quiet think time

• “Discutan con su pareja lo que pensaron” // “Discuss your thinking with your partner.”
• 1 minute: partner discussion
• Share and record responses.

• “¿En qué cosas debemos pensar cuando planeamos una feria del libro para nuestra escuela?” // “What are some things we have to think about if we plan a book fair for our school?” (The different types of books we sell and have to order, the cost of the books for us, the amount to charge for each book, the number of people who come to the fair, and the number of books that we sell.)

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

• Groups of 2
• “Cuando en una escuela se planea vender libros para recolectar fondos, la escuela pide libros de cierto precio a la editorial o a la librería. Luego, los libros se venden a otro precio durante la feria del libro de la escuela” // “When a school plans a book sale fundraiser, the school orders books from the publisher, or bookseller, for a certain price. Then the school sells it for a different price at the book fair.”
• “Imaginemos que en la escuela compran un libro que cuesta \$10. ¿En la feria del libro deberían venderlo por más o por menos de \$10? ¿Por qué?” // “Let’s imagine the school buys a book for \$10. Should they sell the book for more or less than \$10 at the book fair? Why?” (More if they want to make money from the sale.)
• “Este se llama el precio con ganancia. Por cada libro que se venda, la librería obtendrá \$10 y en la escuela se quedarán con el dinero que se le sumó al precio inicial. El dinero que se le suma al precio inicial se llama la ganancia” // “This is called the mark-up price. For every book they sell, the bookseller will get \$10 and the school keeps the amount they added. The amount they add is called the profit.”

• 1 minute quiet think time
• 5 minutes: group work time
• Monitor for students who consider the profit per book in their justifications.

• “¿Cuál es un precio con ganancia razonable?” //“What is a reasonable mark-up price?”
• “¿Qué deben considerar al decidir un precio con ganancia?” // “What do you need to consider when deciding a mark-up price?”

In this activity students 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 through the book sale.

Students will have to make many assumptions in this activity: how many people are coming, how many books each person will buy, and how much to add to the price of the book, to name a few. When students are explicit about assumptions, they model with mathematics (MP4).

• Groups of 2
• “En esta actividad van a planear una feria del libro. La tabla muestra la lista de precios de cada tipo de libro de la editorial” // “In this activity, you’ll plan a book fair. The table shows the price list of each type of book from the publisher.”
• “A veces, cuando planeamos un evento, como una feria del libro, hacemos suposiciones. Las suposiciones son cosas que creemos que van a ser verdaderas basándonos en nuestras experiencias, pero a veces puede que no sean verdaderas. Por ejemplo, podemos hacer suposiciones sobre quiénes podrían venir a la feria del libro” // “Sometimes when we plan something like a book fair, we make assumptions. Assumptions are things we think will be true based on our experiences, but they might not always be. For example, we can make assumptions about who might come to the book fair.”
• “¿Quiénes podrían venir a la feria del libro a comprar libros?” // “Who might come to the book fair and buy books?” (students, parents, grandparents, friends)
• As you plan the book fair, think about other assumptions you make, how they affect the book fair, and how to communicate them in your work.

• 1–2 minutes: quiet think time
• 10–12 minutes: partner work time
• Monitor for students who:
  • Select the types of books based on the kinds of attendees. For example, they select history books because that is something parents want and chapter books which are preferred by students.
  • Make assumptions about the number of attendees and the number of each type of book sold.

• Invite students to share their book sale 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.)