I disagree. Arithmetic (not Maths) is regularly used flying. In the early stages it will be used for flight planning and navigation. In the later stages for fuel calculations, loadsheet preparation, inflight diversions etc. Certainly in the early stages of PPL and CPL it was good enough so that the Nav. computer (circular slide rule etc.) didn't actually have to be used. But you really should have a grasp. But we are talking about simple multiplication, division, addition, subtraction and simple formula rearranging. Nothing that a 12-13 shouldn't be able to deal therefore nothing that you can't teach yourself or whip off the internet.