I don't know if I explained it very well but I'll try to improve a bit. The homework in large classes that have hundreds of students are usually graded online

I don't know if I explained it very well but I'll try to improve a bit. The homework in large classes that have hundreds of students are usually graded online on the book publishers website. For example Pearson publishes a Calculus textbook. In order to do the required homework in class you need to buy a license to the online software which is about $110. The license can only be used once for one book and expires after a set amount of time. So the textbook is not really worth very much. Because it's the license code that is the requirement. I see you were thinking about code as in software. I was talking about a license code. A code similar to the Windows activation code/serial/key etc.