On the generalization of two recreational problems: request for references, if there's any
The first problem is well-known. Lots of different generalizations appear in this paper, which is listed in the Wikipedia entry on the 12 coins problem.

I've never heard of the second problem, but it is similar in spirit to the carrom board puzzle (which probably goes under other names as well), described in a note by Dijkstra. A further generalization appears in this writeup.