Riddle #808

logic

Same Number of Handshakes

At a dinner party, many of the guests exchange greetings by shaking hands with each other while they wait for the host to finish cooking. After all this handshaking, the host, who didn't take part in or see any of the handshaking, gets everybody's attention and says: "I know for a fact that at least two people at this party shook the same number of other people's hands." How could the host know this? Note that nobody shakes his or her own hand.
Assume there are N people at the party. Note that the least number of people that someone could shake hands with is 0, and the most someone could shake hands with is N-1 (which would mean that they shook hands with every other person). Now, if everyone at the party really were to have shaken hands with a different number of people, then that means somone must have shaken hands with 0 people, someone must have shaken hands with 1 person, and so on, all the way up to someone who must have shaken hands with N-1 people. This is the only possible scenario, since there are N people at the party and N different numbers of possible people to shake hands with (all the numbers between 0 and N-1 inclusive). But this situation isn't possible, because there can't be both a person who shook hands with 0 people (call him Person 0) and a person who shook hands with N-1 people (call him Person N-1). This is because Person 0 shook hands with nobody (and thus didn't shake hands with Person N-1), but Person N-1 shook hands with everybody (and thus did shake hands with Person 0). This is clearly a contradiction, and thus two of the people at the party must have shaken hands with the same number of people.
93.39 %
38 votes

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A parrot

A petshop owner had a parrot with a sign on its cage that said "Parrot repeats everything it hears". Davey bought the parrot and for two weeks he spoke to it and it didn't say a word. He returned the parrot but the shopkeeper said he never lied about the parrot. How can this be?
The parrot was deaf.
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Tommy Tucker took two strings and tied two turtles to two tall trees. How many T’s in that?
There are 2 t’s in THAT.
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Shadow drove into the Speedy Service Station and pulled up to the pumps. "Fill it up, please," said Shadow. "This may sound strange," said the owner, "but I'd rather fill two cars from out of town than one car from this town." Shadow looked across the small town and replied, "I know just what you mean." Why would the owner feel this way?
The owner would rather fill two cars from anywhere than one car from town because he would make twice the amount of money.
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Hidden message

Find a short hidden message in the list of words below. carrot fiasco nephew spring rabbit sonata tailor bureau legacy corona travel bikini object happen soften picnic option waited effigy adverb report accuse animal shriek esteem oyster
Starting with the first two words, take the first and last letters, reading from left to right. Example: Carrot fiascO "from these pairs" the message is as follows: CONGRATULATIONS CODE BREAKER
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Identifying a computer's password

A man worked for a high-security institution, and one day he went in to work only to find that he could not log in to his computer terminal. His password wouldn't work. Then he remembered that the passwords are reset every month for security purposes. So he went to his boss and they had this conversation: Man-"Hey boss, my password is out of date." Boss-"Yes, that's right. The password is different, but if you listen carefully you should be able to figure out the new one: It has the same amount of letters as your old password, but only four of the letters are the same." Man: "Thanks boss." With that, he went and correctly logged into his station. What was the new password? BONUS: What was his old password? HINT: It is nine letters long. Also, a "password" can be more than one word...
The old one was: Out of date The new one is: Different He said: My password is "Out of date." And the boss told him the new one when he said: "The password is different."
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There are 100 ants on a board that is 1 meter long, each facing either left or right and walking at a pace of 1 meter per minute. The board is so narrow that the ants cannot pass each other; when two ants walk into each other, they each instantly turn around and continue walking in the opposite direction. When an ant reaches the end of the board, it falls off the edge. From the moment the ants start walking, what is the longest amount of time that could pass before all the ants have fallen off the plank? You can assume that each ant has infinitely small length.
The longest amount of time that could pass would be 1 minute. If you were looking at the board from the side and could only see the silhouettes of the board and the ants, then when two ants walked into each other and turned around, it would look to you as if the ants had walked right by each other. In fact, the effect of two ants walking into each other and then turning around is essentially the same as two ants walking past one another: we just have two ants at that point walking in opposite directions. So we can treat the board as if the ants are walking past each other. In this case, the longest any ant can be on the board is 1 minute (since the board is 1 meter long and the ants walk at 1 meter per minute). Thus, after 1 minute, all the ants will be off the board.
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She fired the new employee on the spot.
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