Textbook Prices Comparing Bookstore Prices to Online Prices

It is Thursday, and I got lots of time to kill before my evening class starts. So I took a little trip to the bookstore and decided to pick some books at random. I wrote down their prices and the ISBN number. Next I went up to my office and searched for them in Amazon dot com. I compared the prices and found the following results:

Mastering the World of Psychology (2nd Edition) (MyPsychLab Series)

• Amazon price $80.56
• Bookstore price $89.17

Psychology (Hardcover)by David G. Myers

• Amazon $92.71
• List Price $107.95
• Bookstore price $117.83

Sociology: A Down-to-Earth Approach (MySocLab Series) (Hardcover)by James M. Henslin

• Amazon $88.46
• List Price $117.33
• Bookstore $117.83

Introduction to Physical Anthropology (Paperback)by Robert Jurmain , Lynn Kilgore , Wenda Trevathan , Russell L. Ciochon

• Both Amazon & List price $107.95
• Bookstore price $100.05

The mark up for Psychology is $10 over the list price. The markup for Sociology is $0.50 over th list price. The Anthropology book I can not figure out.