I've done the aircrew selection for the Fleet Air Arm (and passed..) and from experience the numeracy tests weren't too hard except there's a lot to do in limited time. In fact I missed one set of questions because I didn't read the question paper but still did OK.
Don't worry too much about not doing them all, if its like military aircrew selection they don't expect anyone to do them all but just achieve a certain standard. Obviously the better you do the higher up the list of successful candidates you will be.
Practise is the only way to improve, simple mental exercises like calculating the scores in a game of darts is a good example.
The team test for the RN and RAF (and I assume for Army) look for both team player and leadership qualities. Contributing toward the task at hand instead of sitting back and letting others make decisions; Don't be a wallflower but listen to - and accept - the opinion of others etc.
I wish I was young enough to apply but sadly I'm too old so that's one less competitor!
Anyway, practise, practise, practise and be yourself.
Best of luck to you.