Famous Riddles

Some of the most famous riddles in the world. They’ve been passed down for generations, and are renowned for their ingenuity and universal appeal.

King Octopus and Servants

King Octopus has servants with six, seven, or eight legs. The servants with seven legs always lie, but the servants with either six or eight legs always say the truth.

One day, 4 servants met:
The blue one says: “Altogether we have 28 legs”;
The green one says: “Altogether we have 27 legs”;
The yellow one says: “Altogether we have 26 legs”;
The red one says: “Altogether we have 25 legs”.

What is the colour of the servant that is speaking the truth?

Riddle Answer

Blind Bartender’s Problem

Four glasses are placed on the corners of a square Lazy Susan (turntable). Some of the glasses are upright (up) and some upside-down (down).

A blindfolded person is seated next to the Lazy Susan and is required to re-arrange the glasses so that they are all up or all down, either arrangement being acceptable.

The glasses may be re-arranged in turns subject to the following rules.

  1. Any two glasses may be inspected in one turn and after feeling their orientation the person may reverse the orientation of either, neither or both glasses.
  2. After each turn the Lazy Susan is rotated through a random angle.
  3. At any point of time if all four glasses are of the same orientation, a bell will ring.

Can you devise an algorithm which allows the blindfolded person to ensure that all glasses have the same orientation (either up or down) in a finite number of turns? The algorithm must not depend on luck.

Riddle Answer

The Three Gods

Three Gods A, B, and C are called, in no particular order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter.

Your task is to determine the identities of A, B, and C by asking three yes-no questions; each question must be put to exactly one God. The Gods understand English, but will answer all questions in their own language, in which the words for yes and no are “da” and “ja”, in some order. You do not know which word means which.

  1. It could be that some God gets asked more than one question (and hence that some God is not asked any question at all).
  2. What the second question is, and to which God it is put, may depend on the answer to the first question. (And of course similarly for the third question.)
  3. Whether Random speaks truly or not should be thought of as depending on the flip of a coin hidden in his brain: if the coin comes down heads, he speaks truly; if tails, falsely.
  4. Random will answer “da” or “ja” when asked any yes-no question.

What would your three questions be?

Riddle Answer