I had a lot of these books as a kid. I'm not even 100% why, but my dad glommed on to the idea that they were of high quality, and also quite inexpensive. Probably my favorite was "Higher Mathematics for Beginners" by Yakov Zeldovich[1]. I was a voracious reader, and largely taught myself calculus from it. Another one on probability and statistics I also found quite accessible (can't find it immediately).

There were some other sketchier pop-sci books, I remember one that had the "water has structural memory" theory in it. But likely those didn't do any lasting damage.

[1]: https://mirtitles.org/2022/07/04/higher-mathematics-for-begi...