What Parkfell said..it's numbers ...every day on the line it's dealing with numbers:
Typically stuff like at briefing the following conversation with your colleague:
"This is a bit odd given it's a seven hour sector.. The planners have produced a fuel plan anticipating a total burn of 30 tonnes.. we average a burn of seven tonnes an hour... does that plan look credible to you"? ( => multiplication/division)
Half an hour later:
Lining up for take off is the wind is 45 degrees off runway heading at 30 knots...your crosswind limit is 20 knots - can you do the takeoff? =>( bit of an understanding of trig with a bit of division/multiplication/proportions..)
Half an hour later:
13 miles out from the runway on approach on what should be a 3 degree glideslope, you're at 5000 feet above the airfield........Question from the other seat " does that look right to you?" =>(parkfells 3 times table comes into play )
It's almost all basic arithmetic, but there is no time to use a calculator, (certainly in the last two imagined examples) and if you struggle with basic mental maths it will remove from your capacity to fly the aircraft and might adversly effect your ability to pass a flying course. It's not differential calculus as parkfell says there are certain critical elements that you really do need to have nailed down ..and I would therefore recommend Genghis's advice to somehow re-learn the core topics..