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Brain Teasers and Riddles
Just some good brainteasers and logic problems. You don't have to answer them all. But lets see if we together can all get them eventually. Some are really easy. Others are kind of hard.
1. You drive to work at an average speed of 32 miles/hour. The trip back your average speed was 44 miles/hour.
Is it possible to determine what was your average speed for the whole trip? If so, what was it?
2. A train leaves for Chicago from Detroit. It is traveling 80km/hr. Half an hour later, a train leaves from Detroit to Chicago, it is traveling 60km/hour. Which train will be close to New York when they meet?
3.
Five friends are in a game room. There is a video game which 2 at a time can play. Is it possible to determine who is playing if the following is known? Either Kelly or Henry, or both, are playing. Either Ron or Victor, but not both, are playing. If Amy is playing, so is Ron. Victor or Kelly are either both playing or neither is. If Henry is playing, then so are Amy and Kelly. If it's possible to know for sure, which 2 are playing?
4. In an island there are 2 type of people, knaves and knights. Knaves always lie, and knights always tell the truth.
You encounter 2 people. Person A and Person B.
A: "I'm a knave or B is a knight".
B doesn't say anything.
Determine what A is and what B is (Knight or Knave). If not possible to determine, say so.
5. You are given 3 boxes. 1 box contains a million dollars, the others is empty. If you pick correctly which box has the million dollars, you win the million dollars.
Suppose you pick Box 1. The host then opens Box 3 to show you it's empty, then he asks you if you want to change your choice to Box 2. From a probability aspect, would it matter if you changed your choice or not?
6. You are in a classroom full of 20 students. Everyone has a paper. The teacher says exchange papers with everyone that is shorter than you. How many total exchanges will there be?
7.. You have 2 ropes and a box of matches. You want to measure 60 minutes exactly using only the ropes and the box of matches. Here is what you know:
a) Each rope takes exactly 80 minutes to burn end to end.
b) The rope itself is made out of different material throughout the rope. So, it's rate of burning is not constant throughout the rope.
Can you measure exactly 60 minutes? If so, how?
8.. A King tests 3 logicians. He has 8 hats. 4 Black and 4 White. He asks the logicians to close their eyes. While that is being done, he hides 2 of the hats behind him, and puts 2 hats on each logician. When the logicians open their eyes, they can only see the hats of the other 2 logicians, but can't see their own hats nor the hats the king hid.
The king then starts asking them if they can tell which hate they have on:
Logician A: "No Idea"
Logician B: "Don't know"
Logician C: "Not sure"
The King gets mad, and asks around 1 more time
Logician A: "I still don't know"
Logician B: "I've figured it out"
And he gets it correct. What hats was B wearing and why?
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Re: Brain Teasers and Riddles
[QUOTE]5. You are given 3 boxes. 1 box contains a million dollars, the others is empty. If you pick correctly which box has the million dollars, you win the million dollars.
Suppose you pick Box 1. The host then opens Box 3 to show you it's empty, then he asks you if you want to change your choice to Box 2. From a probability aspect, would it matter if you changed your choice or not?
[/QUOTE]
From a probability standpoint yes.
By the host eliminating 1 choice, you can choose between 2 that it might be and 1 that it isn't, therefore you get an extra 33.3 percent chance,
[QUOTE]6. You are in a classroom full of 20 students. Everyone has a paper. The teacher says exchange papers with everyone that is shorter than you. How many total exchanges will there be?[/QUOTE]
My guess is 0. Both people can't be shorter than another, and if you're the same height there is no exchange.
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Re: Brain Teasers and Riddles
I always liked this one when I was younger: Connect all of the dots using 4 straight lines w/o lifting your pencil.
o o o
o o o
o o o
[QUOTE]My guess is 0. Both people can't be shorter than another, and if you're the same height there is no exchange.[/QUOTE]
That's what I was thinking. I'll look over them more when I get the time.
Edit: Lame, the dots aren't spaced out. If you want to try it, it's much easier if you space em out in a square.
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Re: Brain Teasers and Riddles
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Re: Brain Teasers and Riddles
[QUOTE=AirGauge23]1. 38mph, no?[/QUOTE]
No
[QUOTE]From a probability standpoint yes.
By the host eliminating 1 choice, you can choose between 2 that it might be and 1 that it isn't, therefore you get an extra 33.3 percent chance,[/QUOTE]
Correct
[QUOTE]
My guess is 0. Both people can't be shorter than another, and if you're the same height there is no exchange.[/QUOTE]
Correct
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Re: Brain Teasers and Riddles
[QUOTE]In an island there are 2 type of people, knaves and knights. Knaves always lie, and knights always tell the truth.
You encounter 2 people. Person A and Person B.
A: "I'm a knave or B is a knight".
B doesn't say anything.
Determine what A is and what B is (Knight or Knave). If not possible to determine, say so.[/QUOTE]
Well, if I understand this correctly, no one can say they are a knave. Knaves would have to say they are knights while knights would have to say they are knights as well b/c they always tell the truth. Thus, A is a knave. The or is kinda throwing me off though. I guess I would say B is a knave too because he would be lying about B as well.
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Re: Brain Teasers and Riddles
[QUOTE=Coach A]1. You drive to work at an average speed of 32 miles/hour. The trip back your average speed was 44 miles/hour.
Is it possible to determine what was your average speed for the whole trip? If so, what was it?[/QUOTE]
37.05
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Re: Brain Teasers and Riddles
[QUOTE=GatorKid117]Well, if I understand this correctly, no one can say they are a knave. Knaves would have to say they are knights while knights would have to say they are knights as well b/c they always tell the truth. Thus, A is a knave. The or is kinda throwing me off though. I guess I would say B is a knave too because he would be lying about B as well.[/QUOTE]
No
[QUOTE]
37.05
[/QUOTE]
Correct
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Re: Brain Teasers and Riddles
[QUOTE=Mikaiel]37.05[/QUOTE]
explain.
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Re: Brain Teasers and Riddles
[QUOTE=Doomsday Dallas]explain.[/QUOTE]
You can't do (32+44) / 2 because that would mean you were going at 32 for the exact same time that you were at 44. Let's say you have to drive for 40 miles and you drive the 1st 20 miles at 5 miles/hour and the other 20 miles at 195 miles/hour. Your average speed is gonna be A LOT smaller than 100 miles/hour.
d = distance home-work
t1 = Time between home-work going at 32 miles/hour
t2 = Time between work-home going at 44 miles/hour
speed = distance / time
So :
32 = d / t1
t1 = d / 32
44 = d / t2
t2 = d / 44
x = average speed
x = 2d / (t1 + t2)
x = 2d / (d/32 + d/44)
x = 2d / [d (1/32 + 1/44)]
x = 2 / (1/32 + 1/44)
x = 37.05
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Re: Brain Teasers and Riddles
[quote]In an island there are 2 type of people, knaves and knights. Knaves always lie, and knights always tell the truth.
You encounter 2 people. Person A and Person B.
A: "I'm a knave or B is a knight".
B doesn't say anything.
Determine what A is and what B is (Knight or Knave). If not possible to determine, say so. [/quote]
There are only four cases.
Case 1: Suppose both A and B are knaves. Then one part of A's statement is true, even though B is not a knight. Since his statement has an "or", only one part needs to be true for A to be telling the truth. Hence A is telling the truth. But this contradicts the fact that he's a knave and is supposed to lie. Hence case 1 is impossible.
Case 2: Suppose A is a knave and B is a knight. Then again, A's statement would be a true statement, which contradicts his job, as a knave, to lie. Hence case 2 is impossible.
Case 3: A is a knight, B is a knave. Now both parts of A's statement is false; i.e. A is not a knave and B is not knight. Hence A is lying, and this contradicts the fact that he is a knight. Hence case 3 is impossible.
Case 4: A is a knight, B is a knight. Now A's statement is correct, since B is a knight. This makes sense because A should be telling the truth. Hence both A and B are knights, and this case is the only possibility.
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Re: Brain Teasers and Riddles
[QUOTE=WADE MONEY]
Case 4: A is a knight, B is a knight. Now A's statement is correct, since B is a knight. This makes sense because A should be telling the truth. Hence both A and B are knights, and this case is the only possibility.[/QUOTE]
bingo!
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Re: Brain Teasers and Riddles
[QUOTE=Coach A]
7.. You have 2 ropes and a box of matches. You want to measure 60 minutes exactly using only the ropes and the box of matches. Here is what you know:
a) Each rope takes exactly 80 minutes to burn end to end.
b) The rope itself is made out of different material throughout the rope. So, it's rate of burning is not constant throughout the rope.
Can you measure exactly 60 minutes? If so, how?
[/QUOTE]
We know you can measure 40 minutes by lighting both ends of the rope. So first you light one rope at two ends and the other rope on one end. Then when the first rope burn out, you'll know 40 minutes has passed and the second rope only has 40 more minutes to burn out. If you immediately light the second rope at the other end, that will measure half of 40 minutes which is 20 minutes. That way 40 minutes + 20 minutes = 60 minutes.
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Re: Brain Teasers and Riddles
[QUOTE=sixerfan82]From a probability standpoint yes.
By the host eliminating 1 choice, you can choose between 2 that it might be and 1 that it isn't, therefore you get an extra 33.3 percent chance.[/QUOTE]
I've never bought that though process, I don't understand why just because C has been eliminated as an option it would have any effect on A or B. It seems that after you have eliminated C the choice between A or B would be an independent event from C.
Someone who is good in math could probably explain this, but really from what I can tell it should have no effect.
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Re: Brain Teasers and Riddles
A cowboy rides into town on Friday, stays three days, leaving on Friday? HOW!? OMGZ!
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Re: Brain Teasers and Riddles
[QUOTE=EroticVanilla]I've never bought that though process, I don't understand why just because C has been eliminated as an option it would have any effect on A or B. It seems that after you have eliminated C the choice between A or B would be an independent event from C.
Someone who is good in math could probably explain this, but really from what I can tell it should have no effect.[/QUOTE]
Let's say you picked box A. At 1st, your chance to get the million dollars is 33.3% (1/3).
That means you have a 66.6% chance of picking the wrong box. Which means there's a 66.6% chance the million dollars is either in box B or C.
Since the host tells you it's not in box C, then there's a 66.6% chance it's in box B, so you should switch.
EDIT : Let's say :
Box A : Nothing
Box B : Nothing
Box C : $1,000,000
There's only 3 possible scenarios :
- You pick box A : The host has no choice but to eliminate box B. Switch = win
- You pick box B : The host has no choice but to eliminate box A. Switch = win
- You pick box C : The host will either eliminate box A or B. Switch = fail
So if you switch, you win 66.6% of the time.
And just 33.3% if you don't.
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Re: Brain Teasers and Riddles
[QUOTE=iamgine]We know you can measure 40 minutes by lighting both ends of the rope. So first you light one rope at two ends and the other rope on one end. Then when the first rope burn out, you'll know 40 minutes has passed and the second rope only has 40 more minutes to burn out. If you immediately light the second rope at the other end, that will measure half of 40 minutes which is 20 minutes. That way 40 minutes + 20 minutes = 60 minutes.[/QUOTE]
yep :cheers:
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Re: Brain Teasers and Riddles
[quote=InspiredLebowski]A cowboy rides into town on Friday, stays three days, leaving on Friday? HOW!? OMGZ![/quote]
Ummmmmmmm, the cowboy was Doc Brown? 1.21 JIGGAWATTS!
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Re: Brain Teasers and Riddles
[QUOTE=Mikaiel]Let's say you picked box A. At 1st, your chance to get the million dollars is 33.3% (1/3).
That means you have a 66.6% chance of picking the wrong box. Which means there's a 66.6% chance the million dollars is either in box B or C.
Since the host tells you it's not in box C, then there's a 66.6% chance it's in box B, so you should switch.[/QUOTE]
Your explanation wasn't helpful, but looking it up on Wiki showed me why it made sense.
Though from further reading there seems to be a flaw in your explanation as well, read about it [URL="http://en.wikipedia.org/wiki/Monty_Hall_problem#Probabilistic_solution"]here[/URL]
Edit: Granted in the parameters given in this scenario your right
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Re: Brain Teasers and Riddles
[quote=pete's montreux]Ummmmmmmm, the cowboy was Doc Brown? 1.21 JIGGAWATTS![/quote]
I don't know about all that but I just downloaded a Stevie Ray at Austin City Limits, part from 83 and part from 89. Good ****ing shit.
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Re: Brain Teasers and Riddles
[quote=InspiredLebowski]I don't know about all that but I just downloaded a Stevie Ray at Austin City Limits, part from 83 and part from 89. Good ****ing shit.[/quote]
The horse's name is Friday, derrrrrrrrrrrrrrrrr.
Can't go wrong with Stevie Ray, really. Unless you get some of his late 80's shows where he's high and drunk and plays like shit.
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Re: Brain Teasers and Riddles
[QUOTE=Coach A]
8.. A King tests 3 logicians. He has 8 hats. 4 Black and 4 White. He asks the logicians to close their eyes. While that is being done, he hides 2 of the hats behind him, and puts 2 hats on each logician. When the logicians open their eyes, they can only see the hats of the other 2 logicians, but can't see their own hats nor the hats the king hid.
The king then starts asking them if they can tell which hate they have on:
Logician A: "No Idea"
Logician B: "Don't know"
Logician C: "Not sure"
The King gets mad, and asks around 1 more time
Logician A: "I still don't know"
Logician B: "I've figured it out"
And he gets it correct. What hats was B wearing and why?[/QUOTE]
I'm guessing Logician B looks around and sees that his two other partners are wearing 2 black hats each, or 2 white hats each, thus he determines that he is wearing 2 of the same color as well.
EDIT: Then Logician B can say which color hat he thinks he's wearing, thus giving the other two the answer as to what they're wearing since they know he'd only speak up if he saw them wearing the same colored hat. So if Logician B says "they are both wearing 2 white hats each", they could determine that the King has 2 black hats behind his back, since they could have a look at Logician B and see he is wearing 2 black hats.
Am I anywhere on the right track?
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Re: Brain Teasers and Riddles
And for 3 I'm gonna guess Amy and Ron.
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Re: Brain Teasers and Riddles
[QUOTE=plowking]I'm guessing Logician B looks around and sees that his two other partners are wearing 2 black hats each, or 2 white hats each, thus he determines that he is wearing 2 of the same color as well.
EDIT: Then Logician B can say which color hat he thinks he's wearing, thus giving the other two the answer as to what they're wearing since they know he'd only speak up if he saw them wearing the same colored hat. So if Logician B says "they are both wearing 2 white hats each", they could determine that the King has 2 black hats behind his back, since they could have a look at Logician B and see he is wearing 2 black hats.
Am I anywhere on the right track?[/QUOTE]
Well if that was the case, he would know right away the first time he was asked. But he didn't....you are kind of one the right track...
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Re: Brain Teasers and Riddles
[QUOTE=plowking]And for 3 I'm gonna guess Amy and Ron.[/QUOTE]
No
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Re: Brain Teasers and Riddles
2,3, and 8 remain the only ones un-solved!
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Re: Brain Teasers and Riddles
A women shoots her husband, holds him under water for 5 minutes, and then finally hangs him. Later that evening, they go out an enjoy a lovely dinner.
How can this be?
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Re: Brain Teasers and Riddles
[QUOTE=Bosnian Sajo]A women shoots her husband, holds him under water for 5 minutes, and then finally hangs him. Later that evening, they go out an enjoy a lovely dinner.
How can this be?[/QUOTE]
She took a picture of him.
BTW did anyone get shot-up in you school.
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Re: Brain Teasers and Riddles
[QUOTE=Bosnian Sajo]A women shoots her husband, holds him under water for 5 minutes, and then finally hangs him. Later that evening, they go out an enjoy a lovely dinner.
How can this be?[/QUOTE]
I see what you're trying to do but this little riddle doesn't work.
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Re: Brain Teasers and Riddles
[QUOTE=EroticVanilla]She took a picture of him.
BTW did anyone get shot-up in you school.[/QUOTE]
Nope, apparently the kid will come once the police leave the school, although the police are spying on him 24/7 so I doubt anything will happen.
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Repost the last 3 so i dont gotta find what they are
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Re: Brain Teasers and Riddles
[QUOTE=gino0o]Victor and Kelly[/QUOTE]
Correct!
#2 and #8 are the only unsolved ones
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Re: Brain Teasers and Riddles
[QUOTE=Coach A]
8.. A King tests 3 logicians. He has 8 hats. 4 Black and 4 White. He asks the logicians to close their eyes. While that is being done, he hides 2 of the hats behind him, and puts 2 hats on each logician. When the logicians open their eyes, they can only see the hats of the other 2 logicians, but can't see their own hats nor the hats the king hid.
The king then starts asking them if they can tell which hate they have on:
Logician A: "No Idea"
Logician B: "Don't know"
Logician C: "Not sure"
The King gets mad, and asks around 1 more time
Logician A: "I still don't know"
Logician B: "I've figured it out"
And he gets it correct. What hats was B wearing and why?[/QUOTE]
Because Logician A and Logician C wears the same hat.
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Re: Brain Teasers and Riddles
This word starts with an "e" and ends with an "e", and usually has one letter in it. What's the word?
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[QUOTE=RoseCity07]This word starts with an "e" and ends with an "e", and usually has one letter in it. What's the word?[/QUOTE]
I'm guessing envelope? lol
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Re: Brain Teasers and Riddles
[QUOTE=plowking]I'm guessing envelope? lol[/QUOTE]
Yes. It's a pretty easy one to google.
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Re: Brain Teasers and Riddles
This one is really hard.
Four perfect logicians sat around a table that had a dish with 11 oranges in it. The chat was intense, and they ended up eating all of the oranges. Everybody had at least one orange, and everyone knew that fact, and each logician knew the number of oranges that he ate. They didn't know how many oranges each of the other ate, though. They agreed to ask only questions that they didn't know the answers to.
Their queries are as follows:
A: Did you eat more oranges that I did, B?
B: I don't know. Did you, C, eat more oranges than I did?
C: I don't know.
D figured out how many oranges each person ate.
How many oranges did each person eat?
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Re: Brain Teasers and Riddles
[QUOTE=gino0o]This one is really hard.
Four perfect logicians sat around a table that had a dish with 11 oranges in it. The chat was intense, and they ended up eating all of the oranges. Everybody had at least one orange, and everyone knew that fact, and each logician knew the number of oranges that he ate. They didn't know how many oranges each of the other ate, though. They agreed to ask only questions that they didn't know the answers to.
Their queries are as follows:
A: Did you eat more oranges that I did, B?
B: I don't know. Did you, C, eat more oranges than I did?
C: I don't know.
D figured out how many oranges each person ate.
How many oranges did each person eat?[/QUOTE]
Well, considering they had to ask one another, that means A, B & C all ate less than 5 oranges.
D could easily know if he ate 8 oranges. Greedy bastard.