When I was ten years old at school in England we had a sadistic maths master who would slap you hard in the face if you had trouble with mental maths. That bastard nearly broke my ear drum on one occasion. I have loathed maths ever since that experience, but was just plumb lucky that when I applied to join the RAAF when I was 19 that a mental maths test was not required. It was a simple aptitude test and the real test was sitting in front of the interview board of four RAAF officers one of whom was to become my CO when I got in the RAAF.
The four of them (all wartime pilots) were there to assess your personality and school background (cadet force, enjoyed Rugby and playing cricket etc).
I was assessed as "Unsuitable" but was able to have another go several months later. Logged 10 hours in a Tiger Moth in the meantime which broke my meagre savings, but that impressed the next interview board and was selected for RAAF pilot training after that. Sometimes persistence does pay off. If skill at mental maths had been a criterion I wouldn't be writing this account now.