if its the MOD sample page you were looking at the maths looks to be around GCSE level (which would make sense as for junior ranks of both HM Forces and the Home Civil Service they want GCSE maths or equivalent).
I had a look myself and I did find a couple of the questions “difficult”, simply because I had forgotten some things from high school! Try the BBC’s GCSE revision resources on their education pages (I think they are called Bitesize or something like that).
