Logic Riddles

 
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Question: A man is found dead in a phone booth in a pool of blood. The glass on either end of the phone booth is broken and the phone is hanging. Just outside of the phone booth is a bucket and a stick.

What happened?

Answer: The man was a fisherman and was telling somebody on the phone about the large fish he caught. When he used his hands to gesture how big the fish was he hit the glass breaking it and cutting himself.

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Question: Ants on a stick may only move left or right. If they bump into each other they bounce off of each other and immediately move in the opposite direction maintaining speed the entire time. The only time they change speed is when they fall off of the edge of the stick.

If 25 ants are randomly put on a 1 meter long stick moving 1 meter per second, what is the longest amount of time it could take for them to all fall off?

Answer: The answer is 1 second.

Imagine that each ant is holding a flag and that when an ant bumps into another ant it gives its flag to the other ant. In this way, every ant always has a flag and a flag would never change direction. So each flag would head towards the edge at a rate of 1 meter per second and since the stick is 1 meter long, it would only take 1 second at most for each flag to fall off, and in turn, each ant.

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By lemontart

Question: A very famous chemist was found murdered in his kitchen today. The police have narrowed it down to six suspects. They know it was a two man job. Their names: Felice, Maxwell, Archibald, Nicolas, Jordan, and Xavier.

A note was also found with the body: '26-3-58/28-27-57-16'.

Who are the killers?

Answer: Felice and Nicholas are the murderers. The numbers correspond to atomic numbers on the periodic table of elements: 'Fe-Li-Ce/Ni-Co-La-S'.

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Question: You have a bag with 'N' strings in it. You randomly grab two ends and tie them together until there are no more loose ends.

In the end, what is the expected number of loops (strings tied to their own end)?

Answer: 1 + 1/3 + 1/5 ... + 1/(2N-1).

Each time you tie two together the number of string ends available decreases by 2. The chance of grabbing a string and its end is 1/(2N-1).

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Question: 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.

What three questions can you ask?

Answer: A possible solution is:

Q1: Ask god B, "If I asked you 'Is A Random?', would you say ja?". If B answers ja, either B is Random (and is answering randomly), or B is not Random and the answer indicates that A is indeed Random. Either way, C is not Random. If B answers da, either B is Random (and is answering randomly), or B is not Random and the answer indicates that A is not Random. Either way, you know the identity of a god who is not Random.

Q2: Go to the god who was identified as not being Random by the previous question (either A or C), and ask him: "If I asked you 'Are you False?', would you say ja?". Since he is not Random, an answer of da indicates that he is True and an answer of ja indicates that he is False.

Q3: Ask the same god the question: "If I asked you 'Is B Random?', would you say ja?". If the answer is ja, B is Random; if the answer is da, the god you have not yet spoken to is Random. The remaining god can be identified by elimination.

For more information about the answer visit the following Wikipedia page.

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