Maths vs. "your own logic"...

Argh!! Tomorrow morning (8:30am!!), I have to do a maths test for the first time since 1993.

Revising using GCSE-level text books, I have only vague recollections of formulae, and quirky techniques ("to divide fractions, first invert the fraction you are dividing by, then proceed as with multiplication")...

I have been trying to circumvent the little tricks, and putting faith in the power of "my own logic" - the idea being that surely, if I have a logical mind, I can just work this out. But no... each time I check, I find a tiny flaw in my rationale and I am now having to defer to the ignominy of the GCSE magic tricks...