Hard riddles

interviewlogicmath

Ant and Triangle Problem

Three ants are sitting at the three corners of an equilateral triangle. Each ant starts randomly picks a direction and starts to move along the edge of the triangle. What is the probability that none of the ants collide?
So let’s think this through. The ants can only avoid a collision if they all decide to move in the same direction (either clockwise or anti-clockwise). If the ants do not pick the same direction, there will definitely be a collision. Each ant has the option to either move clockwise or anti-clockwise. There is a one in two chance that an ant decides to pick a particular direction. Using simple probability calculations, we can determine the probability of no collision. P(No collision) = P(All ants go in a clockwise direction) + P( All ants go in an anti-clockwise direction) = 0.5 * 0.5 * 0.5 + 0.5 * 0.5 * 0.5 = 0.25
86.00 %
40 votes

logicmystery

Kidnapped kid

A rich man's son was kidnapped. The ransom note told him to bring a valuable diamond to a phone booth in the middle of a public park. Plainclothes police officers surrounded the park, intending to follow the criminal or his messenger. The rich man arrived at the phone booth and followed instructions but the police were powerless to prevent the diamond from leaving the park and reaching the crafty villain. What did he do?
This is a true story from Taiwan. When the rich man reached the phone booth he found a carrier pigeon in a cage. It had a message attached telling the man to put the diamond in a small bag which was around the pigeon's neck and to release the bird. When the man did this the police were powerless to follow the bird as it returned across the city to its owner.
85.29 %
57 votes

cleanmystery

Mystery of the Ancient Temple

Once upon a time there existed a temple in India which housed three identical idols which spoke to the devotees. The idols were of – God of Truth, which always spoke the truth; God of Falsehood, which always lied; and God of Diplomacy which sometimes spoke the truth and at other times lied. The pilgrims come from all parts of the world to get their questions answered by the Gods. But there was a problem. As the idols were indistinguishable, devotees were not sure from which idol to ask their questions and in turn they did not know which God has answered and whether to believe it or not. Once a wise man visited the temple. He asked the question: "Which God is seated at the centre?" to all the three idols. The idol on the left, centre and right replied God of Truth, God of Diplomacy and God of Falsehood respectively. The wise man at once proclaimed that he had solved the mystery of the temple.
The idols from left to right are: God of Diplomacy, God of Falsehood, God of Truth. The God of Truth is not seated on the left because he always speaks the truth whereas the idol on the left replied that the God of Truth is seated at the centre. The God of Truth is also not seated in the centre as he always speaks the truth but the idol at the centre replied that the God of Diplomacy is seated at the centre. Therefore, the God of Truth is seated on the right. As God of Truth is seated on the right, and he always speaks the truth, then the The God of Falsehood is seated at the centre. The God of Diplomacy is seated on the left and he has lied.
85.04 %
56 votes

cleanfunnylogiclove

Love triangle

A doctor and a bus driver are both in love with the same woman, an attractive girl named Sarah. The bus driver had to go on a long bustrip that would last a week. Before he left, he gave Sarah seven apples. Why?
An apple a day keeps the doctor away!
84.71 %
72 votes

logic

The farmer, the engineer, the physicist, and the mathematician

A farmer challenges an engineer, a physicist, and a mathematician to fence off the largest amount of area using the least amount of fence. The engineer made his fence in a circle and said it was the most efficient. The physicist made a long line and said that the length was infinite. Then he said that fencing half of the Earth was the best. The mathematician laughed at the others and with his design, beat the others. What did he do?
83.05 %
49 votes

logicmystery

Lost jewelry

A couple went on holiday for three weeks. They carefully locked their house, and had a neighbor check on the place while they were gone. When they returned, the wife was distressed to lean that because of a power failure she had lost all her fine jewelry. She had hidden the jewelry in what she thought was a very safe place. She was not robbed. Her jewelry was lost by accident. Why?
In this true incident, the wife had hidden her best jewelry inside her freezer in a bag among all the frozen food. Because of a general power failure the freezer had gone off. A friendly neighbour (who had a key in order to water the plants) had tried to be helpful by throwing out all the bad food - and with it went the jewelry.
82.72 %
48 votes

logicmystery

The Great Wall of China

An American, who had never been to any country other than the United States, travelled a long way to see a sight that very few people had seen. He was standing one day on solid ground when he saw the Great Wall of China with his own eyes. How come?
He was an astronaut standing on the moon - from where the Great Wall of China is visible.
82.37 %
47 votes

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