Re: couldn't even cope with long division or multiplication
My long-suffering bookkeeper despaired of my ability to add up items in my cheque paying-in book. What did amuse her was when the amount was small enough that the bank didn't bother to correct the mistake.
As regards long division and multiplication - I think it depends on the method taught at school. If you moved schools a few times as a child it might be confusing because of differences in teaching, particularly if drummed in by rote.