2 Answers

  1. I think this site will suit you 4brain.ru Russian-language, modern design, a lot of different courses, books and, in general, everything that a person needs who is thinking about self-development.

    And by the way, why did you come up with puzzles? So that people who do not know the mathematical apparatus, too, somehow trained their brains. I have often heard from teachers that in their youth, in their spare time, they solved problems from various collections of problems, for example, from the famous Demidovich – this is self-development!

  2. Of the Russian-language sites with math problems, the site is out of competition problems.ru There are a lot of non-standard tasks of various levels, designed for all ages. True, orientation in it requires some professionalism.

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