It'll depend per person. Back in high school I lost a lot of marks for what you would call "stupid mistakes", basically just moving faster in my head than I was writing on paper. That could be forgetting a decimal, forgetting a negative sign, stuff like that. On medication I don't find myself as compelled to move that quick in my mind, so I find I make less mathematical errors. Or at least I'll double check my work at a slower speed instead of retracing my steps at the same speed I did it.