Amazon sold $120, school sold $200

I received my textbook today, it was only $41 shipping included.

I went to the school bookstore, and saw the price tag on the book shelf, it said New for $199, Used for $149. What the Fxxx!!!

I decided not to buy the book at the school bookstore because my professor didn't give me any assignment.
Some professors require home assingment with textbooks at the first class, so students have to buy the books at the school bookstore.

I went to the Amazon.com as soon as I got home, and I easily found one at $37.

Now, no more $37 books, but still many new books are sold less than $100.

How come my school sell it $200?

I still can not understand!!!!