A fun riddle. Get at it.

Four Dudes in the Sand

Four teammates in a Survivor-esque reality TV show are competing for instant celebrity and $1,000,000,000,000,000,000,000,000,000,000. At the moment, they are buried in the sand, up to their necks.

One teammate is buried on one side of a brick wall, and the other three are buried on the other side of the wall. All of them are facing the wall, and none of them can turn his head. The host of the show has painted X’s on the backs of their heads — white X’s on teammates 1 and 3, and black X’s on teammates 2 and 4.

Because teammate 4 is buried behind teammates 3 and 2, teammate 4 can see the white X on teammate 3, and he can see the black X on teammate 2. Because he’s buried behind teammate 2, teammate 3 can see the black X on teammate 2. Because he’s buried in front of teammates 3 and 4 and facing the wall, teammate 2 cannot see any X’s on anybody. Teammate 1 obviously cannot see any X’s on anybody. None of the teammates has any way of seeing his own X or gaining any information about the color of his X from shadows, reflections in the TV cameras, paint spilled on the ground, etc.

The host tells the teammates that they will be eliminated in an hour unless one of them can figure out the color of his own X. Each teammate knows that there are four teammates total, and each teammate is told that two of them are wearing a white X and two of them are wearing a black X. Each teammate, therefore, knows that his own X is either black or white, but none of them knows which it is.

So, here is what each teammate knows:

Teammate 4: I have either a black or a white X on my head, as do the other teammates. Teammate 2 has a black X on his head, and teammate 3 has a white X on his head.

Teammate 3: I have either a black or a white X on my head, as do the other teammates. Teammate 2 has a black X on his head.

Teammate 2: I have either a black or a white X on my head, as do the other teammates.

Teammate 1: I have either a black or a white X on my head, as do the other teammates.

The team will be given exactly one chance to speak. The first teammate to make a noise must immediately state the color of his own X and explain exactly how he knows what color his X is. If he is wrong about the color of his X, the team will be eliminated. If he says anything that doesn’t explain how he knows what color it is, the team will be eliminated. If his explanation gives the host the impression that he was guessing about the color of his X and got lucky, the team will be eliminated. If all of the teammates remain silent for the full hour, the team will be eliminated.

One of the teammates does figure out the color of the X painted on the back of his head and he is able to give the host a satisfactory explanation for how he knows.

Which teammate figures it out, and what is his explanation?

Advertisements

One thought on “A fun riddle. Get at it.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s