Answer 1
Just the basics, add, subtract, multiply, divide. You'll learn lots of rules of thumb that pilots use, that really eliminates any hard math you'd have to do in your head. For the rest, we have calculators, flight management systems, flight computers, etc. Don't worry about your math skills.
Answer 2You don't need to be a math genius, but you should be able to do the basics well.
Say you've got 26 gallons of fuel on board, you burn 20 gallons an hour, you're ground speed is 100 miles an hour and your 125 miles from the airport. You need to keep at least 30 minutes fuel in reserve.
You need to be able to estimate in your head (without fishing around for a calculator) that you simply can't do it safely and you need to find an airport before you reach your destination.
If you can do this sort of math, you're fine.
Answer 3Add, Subtract, multiply, divide. and really you can get by with just add and subtract when you use a EB6
Answer 4What kind of math? Ratios and interpolation.