Econmics 201
Think about your decision to buy the textbook for this course. You paid $250 for the book, but you would have been willing to pay $400 to use the book for the semester. Suppose that at the end of the semester you could keep your textbook or sell it back to the bookstore. Once you have completed the course, the book is worth only $70 to you. The bookstore will pay you 50% of the original $250.