Saw this on the Independent's website.
http://ind.pn/1QvJYVT It was a problem involving probability that allegedly stumped a large number of students taking a maths GCSE.
It is things like this that mean I never could be a teacher. One look at that problem and jotting down a couple of things on paper, and the answer was obvious. (Except, I was having my breakfast at the time, I wrote the first line of the solution and then when I went back to it I misread a multiplication sign as a plus sign and went down a blind alley.) I don't think I could explain it any simpler.
Indeed some years ago I was at a family gathering for Christmas and my nephew had some A-level maths questions to do. (My nephew is now in his forties, so you can probably work out how long ago this was.) My mother said I could help him. My sister (his mother) said don't be silly, it was over twenty years since I did A-level maths. As it happened, the first problem we looked at involved factorising a polynomial. (I'm sure that was the sort of problem I would have done at O-level, not A-level.) I immediately wrote down the first line of how to solve this and my nephew didn't understand. I tried to exlain, but nothing I said made any sense to him. We stopped the exercise right there and I never helped him with his A-levels again. (Although, when he was at university, I did get a phonecall from him one night, asking me to explain some physics problem, I think it was Compton scattering. But I'd been out at a concert and by the time I got home and he was able to phone me, he'd drunk half a bottle of wine and it was difficult to explain this over the phone.)
I do wonder about the polynomial factorisation whether there was a generation problem. I was of the generation that did not have calculators when at school (except for my trusty slide rule in the sixth form). I was taught long division at primary school and the method I knew for factorising polynomials was based on that. Do children get taught long division these days?
But the upshot is, I think if I was trying to teach maths to someone today, my answer to any question would be, "That's obvious".