Chris,
www.timc.clara.net has some good speed distance time calculations on it. Get some Psychometric testing books, they can help. Fly flight sims if you can, they are reported to give some help. Also practice lots of simple mathmatics, revise all your GCSE maths notes, and try to learn as many variables of 60mph as possible.
For example if you are going at 60 mile an hour thats a mile every minute, 30 miles an hour is a mile every two minutes, 6 miles an hour is a mile every 10 mins etc etc. It can sometimes work out to be easier than doing the whole time = distance/speed x 60/1 routine.
Regards,
Rusty.