Mathemagic
Dozens of number tricks from easy to expert.
Stats for nerds
2recommend
2mentions
2people
2011–2021years
100% recommend
Mentions per year
What Hacker News says
- When I was a kid, I loved the Mathemagic book [1] IIRC this was one of the tricks described in the book.
[1] https://www.amazon.com/Mathemagic-Raymond-Blum/dp/0806983558
- People sometimes guffaw at this, but I can't recommend Donald Duck in Mathemagic Land enough: http://www.youtube.com/watch?v=iEVGQKwKeCc They skip over several centuries of shifting and tweaking between the triad and the modern (western) major scale, but it's a great visual answer at least to your second question.
