[NorthMountain]

550 divided by 2 doesn't have anything to do with algebra or calculus. It's pure arithmetic ... in elementary school I learned (had thoroughly drilled into my head) various techniques for breaking arithmetic problems into easily solved pieces. It's not so much an issue of intelligence (a necessary but not sufficient condition) so much as it is a matter of being properly taught from "Day 1".

it’s just how some peoples mind works spontaneously at a glance.

Yes ... it's indicative of a pedagogical failure in early childhood. What we learn (or don't) in First Grade ... and what we learn at home before we go to school ... REALLY MATTERS. Bad teachers are incredibly destructive. Bad curricula are even more destructive.

[traderrob6]

I disagree. In my case I believe it’s a a fluke, a trick the subconscious mind plays on you until you think about it for a second.

I received my primary education in the 60s and 70’s and would consider the overall quality excellent.