Spring Week Assessments

1) Technically you're probably not supposed to use a calculator but they can't stop you. Although I would practise mental maths anyway because some firms *may* ask you to have a face cam whilst doing the test to make sure you're not using a calculator - that being said I only know of proprietary trading shops like Optiver that make you do this. Its not unheard of for interviewers to throw some sum at you to test your numerical reasoning under pressure either. If you can add and subtract 3 digit numbers in less than around 6-7 seconds you should be fine. Being able to answer questions like 18*16 in around 10s would be good practise too but I haven't heard of them doing this recently in interviews, but they definitely could and have done in the past. Finally if you have an assessment center as a part of the spring week application (and the subsequent conversion during the spring week that I think most do) there's a decent chance you'll do a proctored numerical reasoning test and obviously, no calculator allowed and the score shouldn't be too different from your first one.

2) As for improving; if you can't do the basic operations even with a calculator you're probably not cut out for IB but imo its interpreting the data that can waste time rather than the maths.  I don't think there's an exact hack to this so all I can say is eventually you'll get better at scanning information quickly. - I doubt the actual maths is your issue imho otherwise you wouldn't have passed GCSE maths.

3) Pyschs aren't supposed to be too hard, it just takes practise (ironically enough I don't think practising earlier helps a ton - just do maybe 4 hours of each provider a week before you apply and you should be acclimatised unless you can't do basic maths in which case practise earlier). Apps won't open until September iirc so you have time to chill and do other stuff in the meanwhile.