The Angel Puzzle Answer

March 30

Yesterday we posted this brain teaser: There were four angels on a Christmas tree. Two had a blue halo and two yellow. The angels knew that; they just did not know who had which color. None of them can see their own halo. Angel A is on the highest place, and he can see angels B and C, which hang below him. Below hangs angel B, who can see only angel C under him. Angel C can't see anybody. Angel D can see no one, and no angel can see him. Which one of them can announce what color his own halo is?

Here is the answer!

1. If angels B and C had halos of the same color, then angel A must have immediately said his own color as well as the unseen angel's halo (Angel D).

2. If angels B and C had different colors, then angel A must have been silent, and that would have been a signal for angel B, who could know (looking at angel C) what his own color is (the opposite color of C's halo).