For fans of geometry I can recommend the following book:

Apostol, Mnatsakanian: New Horizons in Geometry : https://www.amazon.com/Horizons-Geometry-Dolciani-Mathematic...

See also: https://en.wikipedia.org/wiki/Visual_calculus

Warning, the comments are spoilers in many cases. :(

It's the convention

These are awesome puzzles!

There are a few problems where I wish they'd be clearer about what the number labels mean. Areas? Edge lengths? They look like they're labeling areas, but I assume that figuring out what the numbers mean isn't intended to be part of the puzzle.

These would make excellent AMC problems. Visually pleasing diagrams, nontrivial uses of similarity, many problems having a “nice” and a “brute-force” solution–all of these fit right in.

Amazing presentation, and just the right difficulty. Thanks for posting this!

Are links to the answers provided?

Here's the twitter link to the first shaded circles one: https://twitter.com/Cshearer41/status/998606724817981441

Toppled square: https://twitter.com/Cshearer41/status/1026837809716518912

Clever.

#3 was particularly elegant, once I saw the trick. I got x=5 for it.