I Was Never Very Good With Numbers

In fact, a lot of what, to you, might be simple mathematics, is to me a baffling confusement.
Maybe there's a numeric equivalent to dyslexia, in which case, I definitely have it.
My father, amongst his other skills, such as putting up sloping bookshelves, and hitting the lawnmower with a big hammer, had a black-belt in accountancy.
He delighted in explaining to me the difficult bits of my maths homework, in an absolutely different way to which my teachers expected me to do it. So even if I'd understood his explanation, I'd have lost marks and been treated with glowering suspicion for getting the right answer the wrong way.
The maths problems I liked involved real world problems... at what point would the two trains meet if....
Or the man digging holes whilst the other bloke was shovelling sand back in...
Or the Parrot with 3 pounds, six shillings and ninepence who wants to buy an off-peak return rail ticket from Cleckheaton to Grimsby, via Kirkwall in the Orkneys, but first has to pay off the compound interest on his ill fated investment in cuttlefish futures.
(Our school textbooks were old and surreal).
In one of those strange twists of fate, I somehow became a teacher, and was somehow qualified to teach mathematics amongst other things.
I learned more maths by teaching it and trying to stay a couple of pages ahead of my charges than I ever did as a pupil. One of the things I enjoyed discovering was that different nations use different methods to do everyday calculations. As also did people here in past times, -the elizabethans had some cunning trickery with grid squares.
So I was delighted to stumble upon this:-