Let's have a brain teaser thread /g/

>>57216882
59 minutes.

59 minutes

>>57216886
>>57216890
Yep.

You got any more Falcon? You do interviews, you probably have some good ones

>>57216901
A riddle I read long ago. Excellent. PLEASE solve on your own (answer available online with ease, but such a waste of mental effort to find it that way).

---

Four missionaries are captured by cannibals. The cannibals will give them a chance to save themselves, failure means getting BBQed.

"In this sack, there are 4 black hats, and 3 white hats. You will be tied up and put in a row, so that each person can only see what is in front. We will pull a hat out at random, and place it on your heads in such a manner that you cannot see what hat you are wearing. Only one of you may speak one word: "White" or "black". If it matches the colour of the hat you are wearing, all four will go free. No other communication of any type is allowed, on the pain of BBQ-death."

The missionaries are tied and lined up, and hatted. Each can see the hats of the people in front, but not their own hat, or the hat of the ones behind.

An hour passes by. Then a second hour. Then a third hour. Then, on the fourth hour, the _first_ person in line (who cannot anyone's hat) figures it out!

What colour was the hat? How did he figure it out?

>>57216951
Another, but not as good.

---

3 guys have dinner outside. The bill is $25. They pay $10 each, and get back five $1 coins. They keep one coin each, and leave $2 as a tip.

As they are walking home, one of them stops and says: "We have been cheated!"

"How?" ask the other two.

"We each gave $10, and took back $1. That is a net of $9 spent per person, or a total of $27."

"Right, the three of us spent a total of $27. And?"

"Well, we also left $2 as a tip, so that is $27 plus $2, for a total of $29! It does not add up! Where did the last $1 go?"

Where did that last $1 go?

---

I am sorry if this one is a groaner. Try it out on your mathematically challenged friends!

>>57216951
Tried this a riddle a few months ago. Got it under 5 mins

>>57217013
lol
Maybe the people on /b/ wouldn't be able to figure out what double counting is.

>>57216951
This one is hard though, I can't figure it out.

>>57216882
It takes 30 minutes. What are you a fucking retard?

>>57216951
black
4th is silent because it aint www infront of him
3rd is silent because it isn ww infront of him
2nd is silent because it is not white infront of him
1st has to have a black hat.

>>57217048
It really isn't. Just imagine yourself in the missionaries' shoes

>>57216951
A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of their own eyes then leave the island, and the rest stay. Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let's say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

"I can see someone who has blue eyes."

Who leaves the island, and on what night?


There are no mirrors or reflecting surfaces, nothing dumb. It is not a trick question, and the answer is logical. It doesn't depend on tricky wording or anyone lying or guessing, and it doesn't involve people doing something silly like creating a sign language or doing genetics. The Guru is not making eye contact with anyone in particular; she's simply saying "I count at least one blue-eyed person on this island who isn't me."

And lastly, the answer is not "no one leaves."

>>57217013
A third one. Slightly unrealistic, but fun.

---

There are two bars on the border of Mexico and the US. Both of these bars accept US and Mexican currency, but each bar favours its local currency, of course! The Mexican bar values USD$1 as $19 Pesos. The US bar value USD$1 as $21 Pesos.

Gonzalez is a math teacher, retired due to alcoholism. A lawful citizen, he can cross the border at will. He has USD$1. He takes the USD$1 to the US bar, where it is worth $21 Pesos. He asks for $20 Pesos, and $1 Peso worth of alcohol. He drinks. Then he takes the $20 Pesos to the Mexican bar (where USD$1 is $19 Pesos) and asks for USD$1, and $1 Peso worth of alcohol. He drinks. When he is drunk enough, he takes his USD$1 and goes home.

How does Gonzalez drink for free?

>>57216882
depends on the size of the jar ;^)

>>57217013
They spent 25 on the bill and 2 on the tip for a total of 27 to the restaurant. They each spent 9, so this adds up

it's a misdirection/word puzzle really

>>57216882
59 minutes.

>>57217113
He exploited the exchange rates to exchange money at a above-market rate?

>>57217113
Eh, not really a riddle. You explained exactly how he did it because of the exchange rates.

>>57217147
>>57217170
There is a riddle in there somewhere. Google offers a better version than what my memory did:

---

The story is told that when the Republic of Texas was feuding with Mexico, there was a law passed by Texas to the effect that a Mexican silver dollar was worth only 50 cents in Texas; whereupon Mexico passed a law that a Texan silver dollar was worth only 50 cents in Mexico. A citizen of Brownsville, Texas, walked across the bridge over the Rio Grande to Matamoros, Mexico, went into a bar, ordered a 50-cent drink of whisky, paid for it with a Mexican dollar and received a Texan dollar in change. He then walked back to Texas, went into a bar, ordered a drink, paid for it with the Texan dollar, and received a Mexican dollar in change. This pleasant pastime, repeated several times a day, went on all winter. At the end of the time the Texan citizen still had his dollar. Obviously the barkeepers suffered no financial losses; and the question is: Who paid for the drinks?

>>57217104
Let us suppose there were only 2 brownies and 2 blueies.

>I see someone with blue eyes

Blue1 looks at Blue2, sees blue eyes. "If my eyes are brown, he will see three brown eyes, and he will leave tonight."

Blue2 does not leave that night.

The second night, Blue1 says to himself: "My eyes are not brown. They must be blue."

Blue1 and Blue2 both leave that night.

---

If we suppose 3 browns and 3 blues:

Night 1: Blue1 sees Blue2 and Blue3. "If my eyes are brown, they will both leave tomorrow."

Night 2: No one leaves.

Night 3: All three Blues leave.

---

For your 100 Blues, it will take 100 days for all the Blues to figure it out, and on the 100th night they will all leave. Unless my logic is off, the Browns leave on the 101st night.

Design an algorithm which finds the smallest matching value in 3 arrays of various sizes. Eg: A[i]=B[j]=C[k]
Do so with at least two threads. Efficientcy counts and the arrays are sorted (because that would be your first step regardless)

Not really a brain teaser but a good interview question.

>>57217268
But he says "there could be 100 brown, 99 blue and one with red eyes"
Otherwise your solution makes sense to me.

>>57217200
The barkeepers did, since they gave someone $1 for $0.5, but the government covered it up. Practically, the economy took the loss.

>>57217104
I guess you could sit through 201 of her speeches and keep count of how many blue or brown eyed people she mentions.

that assumes that she doesn't see the same person twice, though.

>>57217268
Bingo!
What is the quantified piece of information that the Guru provides that each person did not already have?
Each person knows, from the beginning, that there are no less than 99 blue-eyed people on the island. How, then, is considering the 1 and 2-person cases relevant, if they can all rule them out immediately as possibilities?
Why do they have to wait 99 nights if, on the first 98 or so of these nights, they're simply verifying something that they already know?

>>57217373
No, she only says that once ever.

>>57217352
Correct. On the 99th day, all 100 Blues are thinking: "Tonight, either all 99 Blues leave, OR I have blue eyes." No one leaves that night, so on the 100th day, all 100 Blues know they have blue eyes.

>>57216951
4th is quiet because he doesn't see www, this means at least one black in front
3rd is quiet. If he had seen ww he would know he's B. Now it's either wb, bw or bb
2nd is quiet because he sees black and could be either w or b
1st notices this

File: Facepalm Two Guys.png (20KB, 640x461px) Image search: [Google]

20KB, 640x461px

>>57217431
OP here
I'm ashamed how long it look me to realize this

>>57217392
>quantified info
Using a 1blue 1brown starting point: Guru provides full info to 1blue.

With 2blue 2 brown: Guru provides that at least 1blue exists. It takes 1 night of waiting for EachBlue to find that OtherBlue did not leave, therefore there must be at least 2blue.

Also: Browns will never leave. They have no idea that they are brown :(

>>57217490
Muh English! Let me retry.

This is a standard riddle. You have already read it many times, but juuuuuust in case:

---

You have 8 marbles, identical in size and colour. One of them is very slightly heavier, all the rest weigh the same. What is the minimum number of weighings on a balance-scale that is needed to figure out which marble is the heavy one, with certainty?

>>57217431
>>57217082
This can't be correct, there are 7 hats in total. Unless they were lucky enough to pull 3 white hats and all know about it the first guy can't answer the question.
1. W
2. B
3. W
4. B
One of the possible scenarios. What now?

>>57217490
>>57217502
3?

>>57217510
Glad to see someone hear that particular riddle for the first time. You will enjoy it when you understand it.

>>57217510
If this is the case, 2 will know he's the black hatted one and call out, 1 won't have to do nothing.

>>57217502
2
You weight 6 of them, 3v3. If balance, you weight the other two and get the heavier one.
If not, you weight 2 out of the 3 on the same side and follow the same logic

I fuck up sometimes with this question because I forgot to say if it's heavier or lighter

Anyone has anything fresh? I posted 4!

>>57217510
4th quiet because no www
3rd quiet: the 4th would've spoken if he saw www, so if 3 sees ww, he knows he's black.
2nd quiet: 1&2 can't be ww, because 3 was quiet. Could be wb or bw or bb.

If he can see w at this point, 2 could speak, since he must be black. But, he doesn't, so in either of the other possibilities, 1 must be black.

Your scenario would allow 2 to solve the riddle, but 2 didn't solve the riddle, so it can't be the case.

>>57217611
Here's one googled just for you Falcon

You have two light bulbs and a 100-floor building. You want to find the floor at which the bulbs will break when dropped. Find the floor using the least number of drops.

>>57217662
starting at 50, depending if it breaks or not, go up or down half the remaining floors. repeat. ?

>>57217697
I don't actually know the answer, but that's my guess as well.

>>57217715
if i think about it twice, it
cannot be right. there has to be some step where you go up ascending, because you only habe two bulbs. e.g. if it is floor 13 the first two tries will
shatter the bulbs.

>>57217697
>>57217715
The logic is beyond me. If you Googled, can you confirm that a real answer exists?

With 2 light bulbs, and at 11pm local time, I can only get to 25 or 75 floors :(

>>57217662
A lightbulb will definitely shatter from a 2 story fall onto hard ground. So, you drop the first one from floor 1, and if it doesn't shatter try floor 2.
Although, I'm pretty sure even at 1 story a bulb would break.

>>57217781
>>57217785
>>57217761
>>57217747

lol we all got rused

https://pointlessprogramming.wordpress.com/2011/03/11/2-light-bulbs-and-a-100-story-building-solution/

It's that TTH THT problem all over again

>>57217785
With two bulbs, you get a 1-in-3 chance of getting the right floor.

If you do 2 floors at a time, you get the exact floor, but potentially 51 drops, which does not sound optimum.

>>57217822
Wish I had figured it out on my own. I only got 1 step better than the brute force.

>>57216951
If they are standing in the sun the missionaries wearing black hat would have know the answer.

Write a function Brackets(int n) that prints all combinations of well-formed brackets.

For Brackets(3) the output would be
((()))
(()())
(())()
()(())
()()()

>>57216882
(initial volume[b]) * 2^(time in minutes[t]) = (end volume[v])

b * (2^t) = v
b * (2^60) = v
(b * (2^60))/2 = v/2
b * ((2^60)/2) = v/2
b * (2^59) = v/2
time equals 59 minutes

>tfw to intelligent to not show working

>>57216882
30 minutes for the first jar but if you are asking for the second jar it'd be 15 minutes, right?

>>57216951
>Kazuya Hen

>>57219639
nope reread the question

>>57220625
i took an iq test a few years ago and i got a 108. i don't understand this question. can you help me? also was that iq test very wrong?

>>57220675
Lol

>>57220076
was thinking the same.

Anime season 3 fucking when?

>>57216951
I don't get it, if the person behind everyone doesn't see WWW, then there's no hope

>>57217013
I don't even see how this is a riddle. It's more like a story about a retarded person.

>Well, we also left $2 as a tip, so that is $27 plus $2

You're probably telling it wrong

>>57217113
>How does Gonzalez drink for free?
The same way money changers do

File: einstein.jpg (65KB, 500x333px) Image search: [Google]

65KB, 500x333px

>>57222083
woah ur smart u figgered it out bro

>>57222083

A lot of people get caught up in that money one iirc.

>>57219610
>tfw to intelligent to not show working
>to intelligent
>to

>>57217510
In the riddle it is a fact that the front one solved it, don't overthink ik :)