I don't know. My professors didn't care too much about having work done their way, but since I was seeing the material for the first time, I used their method regardless.
As for division, you might want to show work their way, but arrive at the answer your way. If you do work with pen and paper, most professors don't have time to go through every math problem for every student, so as long as your answers are correct and the work is shown, you should be OK.
Good luck.