As the previous poster mentioned, the maths we do while flying is quite simple.
BUT
You really need to have the mental agility to do said simple maths while thinking about a dozen other things. Each separate element of flying is quite simple, but when you put them all together it gets tricky.
The best training I can recommend for real world flying is just general everyday mental arithmetic. Examples:
- Driving to work at 30mph and it's 23 miles, what time will I get there?
- Dinner cost $36.92 for three of us. How much is that each?
- The bank is offering 6% saving rate. If I save $6,000 for three years, how much will I get back?
There's loads of oportunities to sharpen up. The above were easy to do when sitting at a computer with nothing else to do. But what when you're also talking to ATC while reading an approach chart? If you can do the sort of calculations above while having a conversation, then maths while flying will be easy.
HOWEVER
The maths during the initial training (for EASA / JAR and probably for Oz too, not so much for FAA) is much more mind boggling. I did maths up to university level. I'd say that it's not much more difficult than GCSE (English exams at 16) but A-level (exams at 18) maths would be a very good foundation.
On another matter, why are you choosing to do the American license? I'd have thought the Aussie one would be more useful to you.