Paul shows nine colored discs (five red, two blue and two green) to five logicians.

After blindfolding them, Paul picks up the five red discs, sticks one on the forehead of each logician, and hides the other discs elsewhere. After removing the blindfolds, everyone sees the discs (all red) on the others' foreheads but not the one on his own.

After a few minutes, one of the logicians (that reasons a little faster than the others) correctly states the color of his disc. How does he work it out?

The key here seems to be the word "elswhere." I'm guessing that Paul hid the other discs poorly and the logician that guessed correctly spotted them out of the corner of his eye. Or, the blindfolds were of a translucent fabric, which allowed him to easily deduce that his disc was red.  Otherwise, I'd be interested to know how the logician could know with absolute certainty the color of his disc. Or he could have simply made an educated guess, seeing that his other four companions had red discs too.

Posted by Stephen on 2005-09-09 19:02:32