Entropy of any system is state dependent. I just read about thermodynamics and I got this question. I first set my system which contained my classroom, the hallway connecting my physics teacher's cabin and the classroom. Then let the entropy of the system be S when I was going to the classroom in the hall way.(The system conatins me and my teacher in the cabin who is reading a book.) I went to the classroom and took out my book from some bag, scribbled something and put it back in the bag again. Then I just sat there and after sometime took out the book when my teacher came in. He started teaching and I started taking notes. Let the entropy be now S'. Nowe let us take another case. I never put my book inside the bag again. My teacher came in the classroom and I started taking notes. So now we again have the same entropy S'. This means that even if danced around like a fool and then sat back, there should not be any change in the final entropy. So this means that if I calculate the change in entropy between two states, then I cannot tell what happend in between. But things should occur in only one manner or things should change in the system. I am not able to understand where my mistake is. Please help me out on this one.