What he described is one part of three in the computer tests. I shouldn't worry too much about the maths sums if you don't have time (prioritisation and all that). You cannot prepare for it so don't stress too much and just relax. It's supposed to be hard to see how you react under pressure.
Medical will be after stage 3 and before training. Eyesight(very thorough), hearing, urine (only testing for drugs, not booze) and some nasty breathing ones. If you be male then you get your bits felt by the doctor - not the highlight of the day but it's over pretty quick.
Any questions, feel free to PM me