[akg1486]

During IR training there's a fair bit of mental calculations needed in the cockpit to figure out entries in holds. It's not difficult maths, but it does require practice. I have a Masters in Engineering Physics (which includes a LOT of really advanced maths) but that didn't help.

Otherwise it's what's been said above: the math is pretty simple. It's not more difficult on the ATPL level where you use a lot of rules of thumb like the divide-by-three mentioned above.

Becoming a pilot, hobby or professional, requires superficial knowledge about a lot (meteorology, engines, aerodynamics,...) and deep knowledge about nothing.

[David Wood]

And of course it's amazing how much one's (already limited) capacity for mental arithmatic is further eroded by pressure/stress when flying. A good one is "what's the reciprocal track that we need to fly now, Bloggs?" Now, we all know that the reciprocal heading is found by adding or taking away 180 as necessary from the current heading. But it can be damn difficult to calculate that whilst trying to do something else. Hence the value of some simple cheats and yard-sticks.