Here i present solutions of some exercises which I have written during my studies and also some notes. Some of these materials are available only in Polish and some only in English.
Fantastic blog about riddles: http://zagadkowcy.wordpress.com/.
Finite simple group of order 2: http://www.youtube.com/watch?v=BipvGD-LCjU.
My old website with mathematical riddles: http://students.mimuw.edu.pl/~to277393/zagadki/strona.php.