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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ok , thanks ,first :isn't my answer to #23 correct?

second :i found your Talent search today but most of them were solved,the prob is most questions are solved when i'm asleep

Yes you are indeed correct for question 23, but can you explain why changing doors makes your chance 66% instead of 33% clearly and simply, in layman's terms?

PS. There's talent search 4 out, GOGOGO!

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when u get asked for the first time to choose a door ,u have a 33.33... percent chance to get it right (or a simple 1/3) ,now when he opened it and asked u to choose again ,he doubled it to 66.6 (or 2/3) it's not a 1/2 or 50% cz door 3 is open now.

i'm not good at writing an explanation i'm better at speaking .

plus i have help : it's a Monty hall prob. u can get it here

and u can try an interactive game like "translating " it(check it ) here (btw it needs jave to be activated)

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when u get asked for the first time to choose a door ,u have a 33.33... percent chance to get it right (or a simple 1/3) ,now when he opened it and asked u to choose again ,he doubled it to 66.6 (or 2/3) it's not a 1/2 or 50% cz door 3 is open now.

i'm not good at writing an explanation i'm better at speaking .

plus i have help : it's a Monty hall prob. u can get it here

and u can try an interactive game like "translating " it(check it ) here (btw it needs jave to be activated)

Haha, I'm too lazy to read the wikipedia description

The way I see it is this, tell me if it makes sense. feel free to judge me and be like "yo that's whack! makes no sense..."

kk, you have 2 strategies to start with, one is to not care about the opening of the doors and always keep your choice, call this strat A. The other is to pick, and always change your choice once the tv dude opens a door with a goat, call this strat B.

So let's analyze the two strategies.

A: Since you don't care about what door is opened, you always gonna keep your choice, what the presenter opens makes no impact on your choice, or your probability. So it's easy to see the chances are 1/3.

B: Since you will always change your pick, there are two possible outcomes from your first pick:

1. You have 1/3 chance of picking the actual car on your first pick, but since you gonna always swap after the presenter opens a goat, you will end up picking the goat. i.e. 1/3 to pick goat.

2. You pick a goat with 2/3 chance. Since you already got one of the goats, and the presenter has to open a goat, he can only open the other goat, so then only other door left is the car, so when you switch, you will get the car. i.e. you have 2/3 to get the car.

Thus Strategy B wins!! Ya??

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it's weird,cz i thought the same thing when i first read it(REALLY)

and the way that maybe u have picked it from the first time

but the other link in helpful plz check it(it will make it clearer but u have to do it many times,tell me what do u get ) and yes i'm lazy too i din't read the wikpedia thing but bookmarked it and i hate reading on the laptop.

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it's weird,cz i thought the same thing when i first read it(REALLY)

and the way that maybe u have picked it from the first time

but the other link in helpful plz check it(it will make it clearer but u have to do it many times,tell me what do u get ) and yes i'm lazy too i din't read the wikpedia thing but bookmarked it and i hate reading on the laptop.

Ye I've done those java things before, it is 66.66%. I also wrote a script to simulate the game and do the 2 options, ran it like 10000000000000 times lol, the chances are 66.666666%

I think I posted a screen shot of the results from my java program, somewhere above...

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i'm gonna see if i can see your JAVA script .

got to go to bed now,i'll check your Talent search tomorrow,and i just found the java thing i'll try it now if i can

Edited by Hidden G
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i'm gonna see if i can see your JAVA script .

got to go to bed now,i'll check your Talent search tomorrow,and i just found the java thing i'll try it now if i can

Hmmm I dont think I posted the java thing, I will do it tomorrow, cuz it's on my other laptop!

Also I can put money that the talent search questions will be solved by tomorrow morning lol. I've come to realize that people on this forum are ultra smart and dedicated to solving puzzles... We should all open a company, we'll make billionzzzzzzzzzzzzzzzz 　ＧＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＨＡＨＡＨＡＨＡＨＡＫＫＡＨＫＡＫＨＡＫＫ

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8 chains - open all links in 1 chain - \$7

tie all chains together - \$14

Total - \$21

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#2

8 chains - open all links in 1 chain - \$7

tie all chains together - \$14

Total - \$21

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We have 8 chains.

Open all 7 links in 1 chain.

7 chains intact.

Attach 1 open link to each of the other 7 chains on the right.

Money spent = \$21

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We have 8 chains.

Open all 7 links in 1 chain.

7 chains intact.

Attach 1 open link to each of the other 7 chains on the right.

Money spent = \$21

Yes that is indeed correct!

Regarding the game show question, I wrote a simulation and ran it to check the chances, here they are:

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here

Sorry the upload of the image failed.

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Sorry the upload of the image failed.

BUD u post the link i think in page 4 i search for it yesterday and found it it's interesting .

i want to try to learn how to write a java script ,do u know a good website to it?

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If you wanna learn java, hmmmm, I don't know about any good website, I'll try look for some online tutorials that I think are good. But do you know any other object orientated programming languages?

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