Best long riddles

cleanlogicmath

A 400 yard long train, travelling at 30 mph, enters a 4.5 mile long tunnel. How long will elapse between the moment the front of the train enters the tunnel and the moment the end of the train clears the tunnel?
9 minutes and 27.2727 seconds.
77.20 %
47 votes
simplelogicmathcleverclean

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?
Just one.
77.17 %
58 votes
trickycleancrazylogic

A black dog stands in the middle of an intersection in a town painted black. None of the street lights are working due to a power failure caused by a storm. A car with two broken headlights drives towards the dog but turns in time to avoid hitting him. How could the driver have seen the dog in time?
It was daylight.
77.11 %
100 votes
cleansimple

We travelled the sea far and wide. At one time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly. How can that be possible?
The sailors had their backs against either ends of the ship.
77.03 %
41 votes
cleanfunnylogictricky

If a green man lives in a green house, a purple man lives in a purple house, a blue man lives in a blue house, a yellow man lives in a yellow house, a black man lives in a black house. Who lives in a White house?
The President.
76.96 %
52 votes
interviewlogicmath

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
76.96 %
52 votes
logicstory

This teaser is based on a weird but true story from a few years ago. A complaint was received by the president of a major car company: "This is the fourth time I have written you, and I don't blame you for not answering me because I must sound crazy, but it is a fact that we have a tradition in our family of having ice cream for dessert after dinner each night. Every night after we've eaten, the family votes on which flavor of ice cream we should have and I drive down to the store to get it. I recently purchased a new Pantsmobile from your company and since then my trips to the store have created a problem. You see, every time I buy vanilla ice cream my car won't start. If I get any other kind of ice cream the car starts just fine. I want you to know I'm serious about this question, no matter how silly it sounds: 'What is there about a Pantsmobile that makes it not start when I get vanilla ice cream, and easy to start whenever I get any other kind?'" The Pantsmobile company President was understandably skeptical about the letter, but he sent an engineer to check it out anyway. He had arranged to meet the man just after dinner time, so the two hopped into the car and drove to the grocery store. The man bought vanilla ice cream that night and, sure enough, after they came back to the car it wouldn't start for several minutes. The engineer returned for three more nights. The first night, the man got chocolate. The car started right away. The second night, he got strawberry and again the car started right up. The third night he bought vanilla and the car failed to start. There was a logical reason why the man's car wouldn't start when he bought vanilla ice cream. What was it? The man lived in an extremely hot city, and this took place during the summer. Also, the layout of the grocery store was such that it took the man less time to buy vanilla ice cream.
Vanilla ice cream was the most popular flavor and was on display in a little case near the express check out, while the other flavors were in the back of the store and took more time to select and check out. This mattered because the man's car was experiencing vapor lock, which is excess heat boiling the fuel in the fuel line and the resulting air bubbles blocking the flow of fuel until the car has enough time to cool.. When the car was running there was enough pressure to move the bubbles along, but not when the car was trying to start.
76.96 %
52 votes
storydetective

Dave is put in a cell with a dirt floor and only one window. The window is too high for him to reach. The only thing in the cell is a shovel. He won't be able to get any food or water and only has two days to escape or he'll die. Dave can't dig a tunnel because it will take him much longer than two days to do it. How will Dave escape from the cell?
Dave has to use the shovel to create a pile of dirt under the window so he can climb up onto it and escape from the cell.
76.91 %
94 votes
cleanlogiccleversimple

One company had two factories, in different parts of the country, that were making the same style of shoes. In both factories, workers were stealing shoes. How, without using any security, could that company stop the stealing?
Make one factory make the left shoe, and the other make the right shoe.
76.91 %
68 votes