When i was in university i did a math minor. I definitely remember the people who were math majors tended to be fairly bad at simple arithmatic (or at least just very average)
Which may be because you simply can't do everything good without practice and in pure math, well, there are things you don't do as much. When I go back to the 3rd and 4th degree polynoms we solved back in school, it's a hassle. Back then I was quite good at solving them but nowadays it just takes time to get accustomed to these kind of problems.