Topic: Navigation, Flight Planning & Principles of Flight
Whilst you don't need to be brilliant at Maths to fly a plane, it most certainly helps to be at least competent and preferably 'quick' with numbers.
Maths only really becomes 'Maths' when we start doing Algebra and Trigonometry, if we're not using this, chances are we're merely doing basic arithmetic, NOT Maths. Maths is incredibly useful for all aspects of Piloting; Flight Planning (Fuel Calculations), Navigation (Heading, Ground Speed, Wind Velocity, True Airspeed, ROC, ROD). The list is endless!
If Maths isn't your thing, at some point flying will become difficult if not down right dangerous. Over reliance on GPS will come at a cost when it fails and puts you at risk of entering Controlled Airspace unannounced.
At the very least try and get the basics of arithmetic up to scratch and become fast at performing the everyday Pilot calculations.
You're at 4,000 ft and wish to arrive at your destination airfield at circuit height (let's say 1,000ft). At what distance do you commence descent?
A comfortable ROD (rate of descent) for your passengers in a light aircraft is around 500 fpm.
3,000 ft to lose at 500 fpm will take 6 minutes (3,000 / 500).
If your ground speed is 90 knots (1.5 nm per minute), you would need to start descent from 9 nm away, 6nm x 1.5.
If your ground speed is anything else, simply divide it by 60 and multiply this by how many minutes you're descending for. This will tell you how far out to start your descent. You can then mark this on your map to remind you.
Air Traffic Control won't be impressed with you arriving at their zone boundary too high.
This is just one of lots of quick and useful calculations you should be able to do in your head, or at the very least, on the ground before departure. Keep practicing and they'll become a piece of cake.