In first year of college I had math classes, and use of scratch paper was forbidden. (and solving system of 4-5 linear equations on 4cm by 4cm part of paper is

In first year of college I had math classes, and use of scratch paper was forbidden. (and solving system of 4-5 linear equations on 4cm by 4cm part of paper is really interesting resource problem :) I guess math teachers hate reading their students... At least in my college.