Logic

1131 riddles

Riddles that derive from deduction and logical thinking.

At noon and midnight the hour and minute hands are exactly coincident with each other. How many other times between noon and midnight do the hour and minute hands cross?
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Nick timed himself and found out that if he wore a bright white outfit he ran 20 miles in 80 minutes, but when he wore a dark outfit, he ran 20 miles in one hour and twenty minutes. What does this mean for his next race?
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A man ordered a length of rope by telephone from his nearest hardware shop. But when he went to collect the rope, he found that the assistant had written the order incorrectly by interchanging feet and inches. As a result of this, the rope was only 30 percent of the length that the man wanted. What length did he want and what length did he get?
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A mother has three sick children. She has a 24-ounce bottle of medicine and needs to give each child eight ounces of the medicine. She is unable to get to the store and has only three clean containers, which measure 5, 11 and 13 ounces. The electricity is out and she has no way of heating water to wash the containers and doesn't want to spread germs. How can she divide the medicine to give each child an equal portion without having any two children drink from the same container?
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If there is a Yellow house on Bluebird Lane, a Green house on Orange Street, a Pink house on Kitten Road, a Black house on Whitehorse Pike and a Purple house on Firebird hill, where's the White house?
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If seven people meet each other and each shakes hands only once with each of the others, how many handshakes will there have been?
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There is a lamp inside a photography darkroom. When the darkroom door is closed, it is impossible to tell from outside the room whether or not the lamp is on. There are two switches outside the door of the darkroom. One or both of the switches may control the lamp. It also could be that neither of the switches control the lamp. All you know is that the light bulb is currently off and that the lamp and bulb are in working condition. The darkroom door is closed and once you open the door you cannot touch either of the switches. If you can only open the dark room door one time, how can you tell which switches, if any, control the lamp?
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Because cigars cannot be entirely smoked, a hobo who collects cigar butts can make a cigar to smoke out of every 5 butts that he finds. Today, he has collected 25 cigar butts. How many cigars will he be able to smoke?
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Suppose you want to send in the mail a valuable object to a friend. You have a box which is big enough to hold the object. The box has a locking ring which is large enough to have a lock attached and you have several locks with keys. However, your friend does not have the key to any lock that you have. You cannot send the key in an unlocked box since it may be stolen or copied. How do you send the valuable object, locked, to your friend - so it may be opened by your friend?
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Joe bought a bag of oranges on Monday, and ate a third of them. On Tuesday he ate half of the remaining oranges. On Wednesday he looked in the bag to find he only had two oranges left. How many oranges were originally in the bag?
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