/sci/ - Science & Math

My physics professor said that he will not look at anything marked wrongly on an exam if you do not write in pen. Is this fair?

I am just seeing myself in two fucking shitty situations..one where I do the work all properly in pencil and get the right answer and he marks it wrong by his own mistake but then refuses to remark it, and one where I use pen and go through a problem, realize i went about doing it the wrong way, and then have absolutely no fucking space to redo the problem quickly, not to mention scratches and messiness everywhere.

what would be the smartest option?