BrainDen.com - Brain Teasers
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## Question

I'm not sure if these questions have been asked before, apologies if they have:

---1---

You have 4 horses on farm A, and you'd like to move them to farm B. The 4 horses take 1 hr, 2hr, 4hr and 6hr to get from A to B respectfully. Now you can ride a horse and take one horse with you during your journey, and you would travel at the speed of the slower horse. What is the shortest possible time that it will take you to get all 4 horses across?

---2---

I have 8 chains, each chain consists of 7 links. Now I would like to connect all 8 chains into a single loop. It costs \$1 to open up a link, and \$2 to close an opened link again. What is the least amount of money I can spend to create my chain?

---3---

A little girl walks out the house with her little puppy in her arms. She walks 10 meters out. At this instant, her dad walks out the front door to chase after her, she puts her dog down and continues forward. The dad walks at 2m/s and the little girl walks at 1m/s. The dog continuously runs back and forth between the little girl and her dad until the dad catches up to the little girl. The dog runs at 5m/s. How far did the dog run?

---4---

In a room with no windows, only a closed door, there are 3 lightbulbs. You have no way of seeing into the room without opening the door and going inside. Outside there are 3 switches, each corresponds to a lightbulb inside the room but you don't know which. I want to know which switch is for which lightbulb, and I'm only allowed to enter the room once. How would I do it?

---5---

Many years ago, there was a kingdom that had an odd rule. It states that any person on death row has the chance to decide his own fate by pick one of two cards that are faced down. The cards will have one with "Death" written on it, and the other will have "Live" written. If you pick the "Live" card, you get to live. Now one day a person was on death row, the king really really hated him, so he put two "Death" cards faced down on the table for the man to pick. The man still lived afterwards, what did he do?

---6---

(I saw a similar question but this is a little different) There are 13 coins, one is counterfeit. The real coins all weigh the same but the fake is either lighter or heavier than the real ones. You have a balancing scale, you are only allowed to use the scale 3 times, how do you find the counterfeit?

---7---

There's a boat in the harbor, it has a ladder hanging over the edge. The ladder is 10 m long, and the end of the ladder is just touching the surface of the water. The first rung of the ladder is 30 cm above the water, and there's a wrung every 30 cm. The water in the harbor is rising at 50cm/minute. The time now is 10:00 am, when will the water reach the 8th rung?

---8---

There are 10 birds in a tree, I shoot one of them, how many is left? ( EASY PEASY!!!)

---9---

In ancient China, A general called CaoCao knew an attack was coming in the night, so he wanted to keep his soldiers awake throughout the night. He told them that if they could solve this question, then he would grant them all the riches they will ever need and his beautiful daughter's hand in marriage. The question was that he had a farm with 30 chickens, he wanted to kill them all in a week, each day he only kills an odd number of chickens, how should he go about killing the chickens?

---10---

One day, a father went to his three sons and told them that he would die soon and he needed to decide which one of them to give his property to. He decided to give them all a test. He said, "Go to the market my sons, and purchase something that is large enough to fill my bedroom, but small enough to fit in your pocket. From this I will decide which of you is the wisest and worthy enough to inherit my land." So they all went to the market and bought something that they thought would fill the room, yet was still small enough that they could fit into their pockets. Each son came back with a different item. The father told his sons to come into his bedroom one at a time and try to fill up his bedroom with whatever they had purchased. The first son came in and put some pieces of cloth that he had bought and laid them end to end across the room, but it barely covered any of the floor. Then the second son came in and laid some hay, that he had purchased, on the floor but there was only enough to cover half of the floor. The third son came in and showed his father what he had purchased and how it could fill the entire room yet still fit into his pocket. The father replied, "You are truly the wisest of all and you shall receive my property." What was it that the son had showed to his father?

---11---

Pirate Marcelo had been captured by a Spanish general and sentenced to death by his 50-man firing squad. Marcelo cringed, as he knew the Spanish general's firing squad's reputation for being the worst firing squad in the Spanish military. They were such bad shots that they would often all miss their targets and simply maim their victims, leaving them to bleed to death, as the general’s tradition was to only allow one shot per man to save on ammunition. The thought of a slow painful death made Marcelo beg for mercy.

“Very well, I have some compassion. You may choose where the men stand when they shoot you and I will add 50 extra men to the squad to ensure someone will at least hit you. Perhaps if they stand closer they will kill you quicker, if you’re lucky,” snickered the general. “Oh, and just so you don’t get any funny ideas, they can’t stand more than 20 ft away, they must be facing you, and you must remain tied to the post in the middle of the yard. And to show I’m not totally heartless, if you aren’t dead by sundown I’ll release you so you can die peacefully outside the compound. I must go now but will return tomorrow and see to it that you are buried in a nice spot, though with 100 men, I doubt there will be much left of you to bury.”

After giving his instructions the general left. Upon his return the next day, he found that Marcelo had been set free alive and well. “How could this be?” demanded the general. “It was where Marcelo had us stand,” explained the captain of the squad.

Where did Marcelo tell them to stand?

---12---

Once upon a time, in the small magical village, a servant lived with his master who was a wizard. After service of 30 years, his master became ill and was going to die. One day, the master called his servant and offered him for a wish. It could be any wish but just one, and no wishing for more wishes. The master gave him one day to think about it. The servant became very happy and went to his mother to discuss the wish. His mother was blind and she asked her son to wish for her eye-sight to come back. Next, the servant went to his wife. She became very excited and asked for a son as they were childless for many years. After that, the servant went to his father who wanted to be rich and so he asked his son to wish for a lot of money. The next day he went to his master and made one wish through which all the three (mother, father, wife) got what they wanted. What was his wish?

---13---

One snowy night, Sherlock Holmes was in his house sitting by a fire. All of a sudden a snowball came crashing through his window, breaking it. Holmes got up and looked out the window just in time to see three neighborhood kids who were brothers run around a corner. Their names were John Crimson, Mark Crimson and Paul Crimson. The next day Holmes got a note on his door that read “? Crimson. He broke your window.” Which of the three Crimson brothers should Sherlock Holmes question about the incident?

---14---

An 18-wheeler is crossing a 4 kilometer bridge that can only support 10,000 kilograms and that's exactly how much the rig weighs. Halfway across the bridge a 30 gram sparrow lands on the cab, but the bridge doesn't collapse. Why not?

---15---

Two men working at a construction site were up for a challenge, and they were pretty mad at each other. Finally, at lunch break, they confronted one another. One man, obviously stronger, said "See that wheelbarrow? I'm willin' to bet \$100 (that's all I have in my wallet here) that you can't wheel something to that cone and back that I can't do twice as far. Do you have a bet?"

The other man, too dignified to decline, shook his hand, but he had a plan formulating. He looked at the objects lying around: a pile of 400 bricks, a steel beam, the 10 men that had gathered around to watch, his pickup truck, a stack of ten bags of concrete mix, and then he finalized his plan.

"All right," he said, and revealed his object.

That night, the strong man went home thoroughly teased and \$100 poorer. What did the other man choose?

---16---

General Custer is surrounded by Indians and he's the only cowboy left. He finds an old lamp in front of him and rubs it. Out pops a genie. The genie grants Custer one wish, with a catch. He says, "Whatever you wish for, each Indian will get two of the same thing." Custer ponders a while and thinks:"If I get a bow and arrow they get two. If I get a rifle they get two!" He then rubs the bottle again and out pops the genie. "Well," the genie asks "have you made up your mind?"

What did Custer ask for to help him get away?

---17---

What is the next number in the sequence?

1

11

21

1211

111221

312211

13112221

---18---

If a bottle and a cork cost a dollar and a nickel, and the bottle costs a dollar more than the cork, how much does the cork cost?

---19---

You have a lighter and two fuses that take exactly one hour to burn, but they don't burn at a steady rate. For example, one fuse could take 59 minutes to burn the first inch and then burn the rest of the fuse in the last minute. How would you use these two fuses to measure 45 minutes?

---20---

You're riding a horse. To the right of you is a cliff and in front of you is an elephant going the same pace as you and you can't overtake it. To the left of you is a hippo running at the same speed and behind you is a lion chasing you. How do you get to safety?

---21---

You have 50 quarters on the table in front of you. You are blindfolded and cannot discern whether a coin is heads up or tails up by feeling it. You are told that x coins are heads up, where 0 < x < 50. You are asked to separate the coins into two piles in such a way that the number of heads up coins in both piles is the same at the end. You may flip any coin over as many times as you want. How will you do it?

---22---

You are a prisoner sentenced to death. The Emperor offers you a chance to live by playing a simple game. He gives you 50 black marbles, 50 white marbles and 2 empty bowls. He then says, "Divide these 100 marbles into these 2 bowls. You can divide them any way you like as long as you use all the marbles. Then I will blindfold you and mix the bowls and marbles up. You can then choose one bowl and remove one marble. If the marble is white, you live, but if the marble is black...you die.

How do you divide the marbles up so that you have the greatest probability of choosing a white marble?

---23---

Suppose you’re on a game show, and you’re given a choice of three doors. Behind one door is a car; behind the others, goats. You pick a door — say, No. 1 — and the host, who knows what’s behind the doors, opens another door — say, No. 3 — which has a goat. He then says to you,"Do you want to pick door No. 2?" Is it to your advantage to switch your choice? Why?

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## Recommended Posts

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If you have a week to kill the chickens, I assume you have until the time you began on the first day until the same time on the same day the next week. So as long as I have part of this calendar day and part of the same calendar day next week, which give me 8 possible days to kill them. So pick 8 odd numbers that add up to 30, say 5,5,5,5,3,3,3,1.

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Change your door. You had a 1/3 chance of winning, by switching your odds change to 2/3. You double your chances of winning. Believe it!

You had 1/3 chance to begin with, when you change doors, your chances are increased to 1/2 NOT 2/3.

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If you have a week to kill the chickens, I assume you have until the time you began on the first day until the same time on the same day the next week. So as long as I have part of this calendar day and part of the same calendar day next week, which give me 8 possible days to kill them. So pick 8 odd numbers that add up to 30, say 5,5,5,5,3,3,3,1.

Sorry, Akariass's answer was correct. It is 7 days, not 8.

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Hmmm, how about he wishes for the genie to beat him half to death.

Hahahaha I like that...

Give him a glass eye.

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My first thought was that he had them stand in a circle. So they would kill each other. But could he have had them stand behind the post he was tied to? So they would only hit the post if they got lucky?

Your initial thought was right, make them all stand in a circle and the firing squad would be too afraid to fire as they make shoot each other in the process

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As a matter of fact, almost all of these riddles have been posted before. There are a few new ones, however.

I don't think it's possible, since you're asking to have 7 odd numbers sum to an even number, which is impossible no matter what you do.

I would guess that he asked for their wishes to be granted.

For 12, he cannot ask more wishes or wishes of others to be granted. He has to wish for something that will fulfill all their wishes.

C'mon guys, still got 6, 12, 21 and 22 to do!

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A spice or scent of some kind.

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A spice or scent of some kind.

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He arranged them in a circle around him.

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\$21 - Open all of the links in one 7 segment chain and use them to join the remaining 7 chains.

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He wished that the wishes of his mother, wife and father be granted.

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He wished to have the same powers as his master.

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Whatever door you initially choose, the game show will open a door with a goat behind it initially, whether you have the one with the car or not. So there is no advantage to switch since you will have the same choice whatever door you initially chose.

You are mistaken, draw out the scenario and you'll find out why.

Edited by Rodrigo
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I have to say that twinhelix did a great job coming up with all these puzzles.

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I have the solution for 6. But i can only identify the counterfeit coin and cannot tell whether it is lighter or heavier.

Will it do? If yes, i can post my solution here.

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I have the solution for 6. But i can only identify the counterfeit coin and cannot tell whether it is lighter or heavier.

Will it do? If yes, i can post my solution here.

Yes that's perfect, you can't identify whether the coin is heavier or lighter in all cases. Only in some.

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"I wish my mother could watch my son climbing on my father's piles of money"

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Actually, for question 23

I was incorrect in saying the chances are changed to 1/2, the other guy was right, it is 2/3. I ran a simulation and checked haha...

http://imgur.com/kryzJ
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He could tell them to stand on their weapons

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If you cut one of the 8 chains apart into 7 open links that eliminates one chain. Use the seven links to join the 7 remaining lengths into a loop. The total cut is \$1 x 7 and closed \$2 x 7 for a total of \$21 to make the loop of chains with a total of 8 X 7 = 56 links.

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The time it takes the dad to catch his daughter times the avg speed of the dog is correct, but this is not just for the initial 10 meters. By the time dad has gone 10 m his daughter has gone another 5 m. It takes dad another 2.5 sec to cover that distance and in the mean time the girl moves forward half that distance as well. I used a spread sheet to calculate 62 levels of micro seconds and totaled the column. It totaled 10 seconds. In the 10 seconds it took dad to catch his daughter, at 5m/sec the pup would have covered 50 meters total going back and forth between them (with no lag time for turn arounds, this being covered in it average speed).

Edited by Magi-Ken
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I have seen some questions on this but no steps for doing it yet so I think that is in order as part of the answer. However, I am not sure I have THE answer because I need a clarification in what USE THE SCALES 3 times means. Based on that I have 2 answers. The first is 100% and ALWAYS tells if the fake coin is lighter or heavier. The second does not work infallibly.

Solution #1: Start placing one coin on each side of the scale and keep adding one coin to each side, keeping track of the two coins added last. As soon as the balance is unequal one of the two last coins is fake. Remove those two and set them aside. If you hold the odd 13th coin and the scales still balance at 6 coins on each side then you hold the fake. Balance used once; clear the scale. The second time place one of the two suspect coins on one side and any of the non-suspect coins on the other side. If they balance then the other suspect coin is the fake. If they do not balance the suspect coin on the balance is the fake one and is obviously heavier or lighter than the non-deviant/non-suspect one. Use number three of the scale is only if they balance in step 2 and is used to verify (not determine) whether or not the fake is lighter or heavier, but even this would not be needed if one kept track of which side was heavier in step #1.

Solution #2 takes "use the scales" as meaning -- each time a coin or coins are added or removed this counts as one use. In that case, remove one coin and set it aside. Place 6 of the 12 remaining coins on each side. If they balance - Lucky YOU! - You held out the fake and have a good eye or 6th sense. Weigh it against any of the others and you will confirm it is different and know if it is lighter or heavier. However, if the 12 coins do not balance. the coin you held out is a good one. Since you do not know which set of 6 has the light or heavy coin the 2nd use is a 50/50 guess remove the 12 keeping them in distinct piles of 6. Put one group of 6 back on the scale; three on each side. If they balance, you can't do it in three steps by this method. If they do not balance, you have narrowed it down to 1 of 2 groups of 3. If the first test showed this group to be heavier then you are looking for a heavy coin. If test #1 showed it lighter then a lighter fake. The third use is to hold out one of the 3 coins from the group of 3 that has the fake (you know which group of 3 that is because you know it to be lighter or heavier). Set your new choice of one of the three aside and weigh the remaining 2. If these 2 balance you picked out the fake. If they don't balance, then the fake is the one that is consistant with your known lighter or heaver weight. The only time this does not work is if you pick the wrong pile of 6 to test. In that case, your groups of 3 will balance and it will take an extra step to go back and divide the other set of six into 2 sets of 3 etcetera.

If there is a better, more clever solution, I am anxious to hear it. It will be exciting.

Edited by Magi-Ken
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I too thought of having them stand on their guns. Either that or very tightly pressed together around him so that they could not even lower or raise their weapons and those in the front became human shields. Firing would then have to be in the air except possibly for those in the outer parimeter. So standing with two feet ON their guns; one foot on the stock and the other on the barrel with the rifle on the flat even ground at the same level as the foot of the pole would be safest request. He could even use being tied to the pole to his advantage if he could raise his feet from the ground at the command to fire in case some got clever and figured out how to pull the trigger. A ridiculous scenario at best in any case, so why not combine the two and now everyone should be safe.

Edited by Magi-Ken
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The General did not want a solution. He only wanted to keep his men awake all night and ready for the impending attack. The answer is not in solving the puzzle, but in the time it takes to figure out the offer or marriage and riches were a rouse, there is no answer.

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What do you fear most? What is SAFETY? I have to know that before I can say what to do to be safe. Do you most fear being eaten by the lion? And are you relatively unafraid of the cliff, the hippo, and the elephant? Since many riddles are quirky, here is my quirky answer based on that case.

Stand up (trick-rider style) on your horse and as you jump onto the back of the hippo yank on the reigns and shout "Woah!" Your hopes are A) your horse stops and appeases the lion's appetite so you can get away, B) you do not spook the hippo into cliff diving, C) you can actually ride a wild hippo and it will not throw you off and trample you. OR if you have a horse, why not a gun, If you can't get a bead on the lion shoot the hippo right next to you and let him be the lion's meal. Just beware the cliff and hope the big fellow rolls away from you and your trusty steed. Hey, anybody have a better answer to this hypothetical?

Along that line of "reasoning": How do you get down from a charging hippo? Answer; You don't. You get "down" from a duck or goose. Some say that is because they are much shorter and easier to get off of if you ever happen to be sitting on one in the first place -- rimshot --(Can you tell it is late am I am tired?)/spoiler]

Edited by Magi-Ken

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