Forehead Numbers Brain Teaser of Khan Academy
Today I remembered a little brainteaser I saw on Khan Academy quite a while back: Khan Academy Link or Youtube Link What surprises me though is that people still seem to think that there are values for which this can not be solved. My conjecture is that it CAN be solved for all 3-tuples of numbers provided that the participants know that they are unique. I would recommend seeing the teaser and understanding the logic behind it before reading further. 3 years ago, when I first saw this, I posted a reply on Youtube describing the same 'game' from the perspective of a player who sees 15 and 11. For the sake of simplicity we'll call the player with 15 A and the one with 11 on his forehead C. Therefore the game is described from the perspective of B: A-pass B-pass C-pass A-pass B-pass C-pass A-pass B-pass C-pass A-figures out his number (15) B-figures out his number also C-figures out his number as well (11) The question then is, what is B's number (