Anyone have any good riddles or brain-teasers to share?

[purbeast0]

Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

Another one from an interview:
You have 2 fuses that each take 60 minutes to burn. There is no guarantee that they burn uniformly. It may take 59 minutes to burn 1% of the fuse, then 1 minute to burn the other 99% of the fuse. Or it could take 30 mins to burn 50% of the fuse, and 30 mins to burn the other 50% of the rope. There is no guarantee regardless.

Also you have no way to tell time or to tell when a specific amount of time has passed. You do not have a watch or clock with you, and you cannot just "count" out a certain amount of time.

How do you burn the fuses to guarantee they will burn in exactly 45 minutes.

 

[dullard]

Originally posted by: DaShen
How is this only 2%?

All you have to do is write it down and build a matrix logic algorithm to figure out who is who. I see bird, dog, cat, and horse... so the last one would be fish. (it doesn't look that difficult).

It is a simple plug and chug problem. The reason it is only 2% is because only 2% have been shown the simple and straightforward solution method. This is a test of what you have been taught, not of your ability nor of your intelligence. I suppose it is partly a test of whether you care enough as well though.

Also, I doubt if the 2% number was scientifically measured. It may not really be 2%.

 

[jhayx7]

A man is asleep in his bed and is woken by a noise in his house. He gets up and goes into the living room and finds that there is a robber exiting the front door. The man runs outside after the burgler but stops when he realizes that he knows the burgler. How can this be possible when there are no lights on in the house or streetlight, it was a new moon (thus no moonlight) and the robber did not make a sound.

 

[DaShen]

Originally posted by: Garet Jax
You have nine balls. 8 are physically identical in weight and dimensions. 1 is the identical dimension as the others, but is a different weight.

You have an equal arm balance and are allowed 3 weighings. How do you determine the 1 ball that is different than the other 8 and whether it is heavier or lighter than the other 8.

4 on one hand 4 on other (choose heavier or lighter)
2 on one hand 2 on other (choose heavier or lighter)
1 on one hand one on other

This only works if you are allowed more weighings though.

1) 4 on one hand 4 on other (drop one on each side)
2) If remaining weigh the same, dropped balls must be weighed to determine
3) If remaining on each hand are still different, drop one on each side again
Repeat from 2

This one works better but still has a chance to have more weighings.

 

[DaShen]

Originally posted by: BigJ

Originally posted by: DaShen

Originally posted by: dopcombo
Er, you nail the wooden planks in a T shape and place the structure at the corner of the lake?

NICE :thumbsup:

If you're going to the Hardware store to get a hammer and nails, you might as well pick up a big ass ladder too

you don't need nails.

 

[dullard]

Originally posted by: purbeast0
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

Because I like to poke holes into riddles, here is my answer. They all decide within the room that they quit their job. Heck, if they have phones, they call their employer and quit or if they have writing utensils they write notices that they quit. Then they leave knowing their average salary is $0.

 

[thecrecarc]

Originally posted by: jhayx7
A man is asleep in his bed and is woken by a noise in his house. He gets up and goes into the living room and finds that there is a robber exiting the front door. The man runs outside after the burgler but stops when he realizes that he knows the burgler. How can this be possible when there are no lights on in the house or streetlight, it was a new moon (thus no moonlight) and the robber did not make a sound.

it was daytime?

 

[purbeast0]

Originally posted by: dullard

Originally posted by: purbeast0
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

Because I like to poke holes into riddles, here is my answer. They all decide within the room that they quit their job. Heck, if they have phones, they call their employer and quit or if they have writing utensils they write notices that they quit. Then they leave knowing their average salary is $0.

lol sorry, wrong

 

[DaShen]

Originally posted by: dullard

Originally posted by: allisolm
That'll give you a pile of 4 unknown balls and another pile of 4 balls known to be the same weight.

but there are 9 balls.

Oops. I misread it as 8 balls. Let me retype it. Fixed:

Originally posted by: Garet Jax
You have nine balls. 8 are physically identical in weight and dimensions. 1 is the identical dimension as the others, but is a different weight.

1) Weigh any 3 unknowns vs any 3 unknowns.
1a) If they are equal, you?ll have 3 unknowns and 6 equals.
1b) If they are unequal, you?ll have 3 light, 3 heavy, and 3 equals. Skip to step #4

2) Weigh the 3 unknowns vs any 3 equals.
2a) If the 3 unknowns are light, you know the odd ball is light.
2b) If the 3 unknowns are heavy, you know the odd ball is heavy.

3) Thus take any one of the unknown balls vs another unknown ball. If these are equal, the ball you didn't weigh was the odd ball. If those two are unequal, the one that matches the heavy or light side is the odd ball. Problem solved.

4) Weigh 3 light vs 3 equals.
4a) If they are equal, you know the odd ball is heavy. You'll also have a pile of 6 equals and a pile of 3 unknowns. Go to step #3.
4b) If they are unequal, you know the odd ball is light. You'll also have a pile of 6 equals and a pile of 3 unknowns. Go to step #3.

There are much more difficult versions of this problem. I'm glad you gave an easy to type answer version.

That is a cool solution

**EDIT**
DANG IT, OP. Why did you have to post this? I am already behind from yesterday at work. Logging off now.

 

[Born2bwire]

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

EDIT: Pretty much I would imagine that there are a variety of ways you can encode one's salary with another piece of information. Like instead of ages, why not use house numbers or some other numerical information generally unique to an individual that is not readily discernable from their appearance.

 

[jhayx7]

Originally posted by: thecrecarc

Originally posted by: jhayx7
A man is asleep in his bed and is woken by a noise in his house. He gets up and goes into the living room and finds that there is a robber exiting the front door. The man runs outside after the burgler but stops when he realizes that he knows the burgler. How can this be possible when there are no lights on in the house or streetlight, it was a new moon (thus no moonlight) and the robber did not make a sound.

it was daytime?

:thumbsup:

 

[artikk]

Originally posted by: jhayx7
A man is asleep in his bed and is woken by a noise in his house. He gets up and goes into the living room and finds that there is a robber exiting the front door. The man runs outside after the burgler but stops when he realizes that he knows the burgler. How can this be possible when there are no lights on in the house or streetlight, it was a new moon (thus no moonlight) and the robber did not make a sound.

He knows the burglar because the robber exited the front door, suggesting that he lived or knows the house, aka family/relative. A real(stranger) burglar would leave using the back door to not avoid getting caught, it would seem.

 

[purbeast0]

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

 

[Born2bwire]

Originally posted by: purbeast0

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

No, he only knows his own age. Like I said, one could make the argument that you could discern age from one's appearance. But you could easily choose a number that would have no bearing. Even better, the last four digits of your SSN. So the guy looking at the slips only knows his salary and SSN, and only has either the sum of the salary and SSN or the last four digits of an SSN but he does not know which one is associated with which individual.

 

[Garet Jax]

Originally posted by: DaShen

Originally posted by: Atheus
Einstein's riddle. Apparently only 2% of the population can solve it.

1. In a street there are five houses, painted five different colours.
2. In each house lives a person of different nationality
3. These five homeowners each drink a different kind of beverage, smoke different brand of cigar and keep a different pet.

Hints:

1. The Brit lives in a red house.
2. The Swede keeps dogs as pets.
3. The Dane drinks tea.
4. The Green house is next to, and on the left of the White house.
5. The owner of the Green house drinks coffee.
6. The person who smokes Pall Mall rears birds.
7. The owner of the Yellow house smokes Dunhill.
8. The man living in the centre house drinks milk.
9. The Norwegian lives in the first house.
10. The man who smokes Blends lives next to the one who keeps cats.
11. The man who keeps horses lives next to the man who smokes Dunhill.
12. The man who smokes Blue Master drinks beer.
13. The German smokes Prince.
14. The Norwegian lives next to the blue house.
15. The man who smokes Blends has a neighbour who drinks water.

WHO OWNS THE FISH?

How is this only 2%?

All you have to do is write it down and build a matrix logic algorithm to figure out who is who. I see bird, dog, cat, and horse... so the last one would be fish. (it doesn't look that difficult).

I read through this quickly and it looks more like a trial and error problem that a logic problem.

A logic problem should be able to progress from start to finish with no missteps unless there was an error in the logic.

A trial and error problem is one where the only way to get to the right solution with no errors is through a miracle.

Trial and error problems suck....

 

[BigJ]

Originally posted by: purbeast0

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

1, 0, and -1 are all on 3 different slips of paper.

Each man takes a slip of paper and adds the number to their salary. They then add up all of the modified salaries and divide by 3.

 

[Born2bwire]

Originally posted by: Garet Jax

Originally posted by: DaShen

Originally posted by: Atheus
Einstein's riddle. Apparently only 2% of the population can solve it.

1. In a street there are five houses, painted five different colours.
2. In each house lives a person of different nationality
3. These five homeowners each drink a different kind of beverage, smoke different brand of cigar and keep a different pet.

Hints:

1. The Brit lives in a red house.
2. The Swede keeps dogs as pets.
3. The Dane drinks tea.
4. The Green house is next to, and on the left of the White house.
5. The owner of the Green house drinks coffee.
6. The person who smokes Pall Mall rears birds.
7. The owner of the Yellow house smokes Dunhill.
8. The man living in the centre house drinks milk.
9. The Norwegian lives in the first house.
10. The man who smokes Blends lives next to the one who keeps cats.
11. The man who keeps horses lives next to the man who smokes Dunhill.
12. The man who smokes Blue Master drinks beer.
13. The German smokes Prince.
14. The Norwegian lives next to the blue house.
15. The man who smokes Blends has a neighbour who drinks water.

WHO OWNS THE FISH?

How is this only 2%?

All you have to do is write it down and build a matrix logic algorithm to figure out who is who. I see bird, dog, cat, and horse... so the last one would be fish. (it doesn't look that difficult).

I read through this quickly and it looks more like a trial and error problem that a logic problem.

A logic problem should be able to progress from start to finish with no missteps unless there was an error in the logic.

A trial and error problem is one where the only way to get to the right solution with no errors is through a miracle.

Trial and error problems suck....

I was able to do this without any trial and error. There is enough information in the problem to determine all the assignments without guessing.


EDIT: BigJ, oooh, that's another good way of doing it too.

 

[purbeast0]

Originally posted by: Born2bwire

Originally posted by: purbeast0

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

No, he only knows his own age. Like I said, one could make the argument that you could discern age from one's appearance. But you could easily choose a number that would have no bearing. Even better, the last four digits of your SSN. So the guy looking at the slips only knows his salary and SSN, and only has either the sum of the salary and SSN or the last four digits of an SSN but he does not know which one is associated with which individual.

You are on the right track but I feel you aren't explaining it clearly. You basically said each person writes the following on a piece of paper.

1. Total of salary + SSN
2. SSN

They then hand that paper to 1 person, and that 1 person adds them all up then subtracats. However since he now has the other 2 people's paper, he can subtract the SSN from the total, resulting in the salary. It doesn't matter if he knows who's is who's, because he still knows the exact salary of the other 2 guys in the room.

They cannot know the exact salaries at all.

 

[Garet Jax]

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

Another one from an interview:
You have 2 fuses that each take 60 minutes to burn. There is no guarantee that they burn uniformly. It may take 59 minutes to burn 1% of the fuse, then 1 minute to burn the other 99% of the fuse. Or it could take 30 mins to burn 50% of the fuse, and 30 mins to burn the other 50% of the rope. There is no guarantee regardless.

How do you burn the fuses to guarantee they will burn in exactly 45 minutes.

1st)

Have the first guy choose some random number and then add his salary to it. Write it down. Pass the paper to the second guy who adds his salry to the number on the paper and writes it on a new piece. The third guy adds his salary to the number on the latest paper and then writes it down. He passes the paper to the first guy who subtracts the random number he added to start. Divides by 3.

2nd)

I will have to think a little more about it.

 

[purbeast0]

Originally posted by: BigJ

Originally posted by: purbeast0

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

1, 0, and -1 are all on 3 different slips of paper.

Each man takes a slip of paper and adds the number to their salary. They then add up all of the modified salaries and divide by 3.

When they add the guy's salary who had the 0 on his paper, they will now know one of the other guy's exact salaries.

 

[dullard]

Originally posted by: purbeast0
You are on the right track but I feel you aren't explaining it clearly. You basically said each person writes the following on a piece of paper.

1. Total of salary + SSN
2. SSN.

No, he said write those on two completely different pieces of paper which are then scrambled. How can you know which SSN or which age to subtract after they are scrambled?

 

[BigJ]

Originally posted by: purbeast0

Originally posted by: BigJ

Originally posted by: purbeast0

Originally posted by: Born2bwire

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

They write down on different slips of paper the sum of their salary and age and just their age. Then one person adds up the sums of salary and ages and subtracts the individual ages and divides by three.

if they write their age on that slip of paper with the age + salary, then the guy who does the total math will know the individual salaries because he can subract it before he ads them.

1, 0, and -1 are all on 3 different slips of paper.

Each man takes a slip of paper and adds the number to their salary. They then add up all of the modified salaries and divide by 3.

When they add the guy's salary who had the 0 on his paper, they will now know one of the other guy's exact salaries.

They know one of them is an exact salary, but they don't know who it belongs to. I guess it's all in the wording.

 

[Garet Jax]

Originally posted by: DaShen

That is a cool solution

**EDIT**
DANG IT, OP. Why did you have to post this? I am already behind from yesterday at work. Logging off now.

If you think this one was good, then try it with 12 balls. Identical problem.

 

[purbeast0]

Originally posted by: Garet Jax

Originally posted by: purbeast0
Here's one from an interview I had:
You have 3 guys in a room. No one can know the salary of what the other people makes, however when they all leave the room, they must know the average salary of the 3 people in the room. How do they do this?
(and remember, no one can know anyone elses salary).

Another one from an interview:
You have 2 fuses that each take 60 minutes to burn. There is no guarantee that they burn uniformly. It may take 59 minutes to burn 1% of the fuse, then 1 minute to burn the other 99% of the fuse. Or it could take 30 mins to burn 50% of the fuse, and 30 mins to burn the other 50% of the rope. There is no guarantee regardless.

How do you burn the fuses to guarantee they will burn in exactly 45 minutes.

1st)

Have the first guy choose some random number and then add his salary to it. Write it down. Pass the paper to the second guy who adds his salry to the number on the paper and writes it on a new piece. The third guy adds his salary to the number on the latest paper and then writes it down. He passes the paper to the first guy who subtracts the random number he added to start. Divides by 3.

2nd)

I will have to think a little more about it.

ding ding with the 1st one! that was exactly what I said in the interview, however they then gave me a much simpler answer. Everyone just adds an arbitrary # to their salary. They then add these 3 numbers up. They then each subtract their 3 numbers from the total and divide it by three.

It was basically about encryption.

And it's very similar to what these other guys were saying too, but it was just a little off.

 

[Thraxen]

Originally posted by: purbeast0

You are on the right track but I feel you aren't explaining it clearly. You basically said each person writes the following on a piece of paper.

1. Total of salary + SSN
2. SSN

They then hand that paper to 1 person, and that 1 person adds them all up then subtracats. However since he now has the other 2 people's paper, he can subtract the SSN from the total, resulting in the salary. It doesn't matter if he knows who's is who's, because he still knows the exact salary of the other 2 guys in the room.

They cannot know the exact salaries at all.

What if they write the salary + SSN on different pieces of paper and then drop that into a bag and shake it up. Then one person pulls them and adds up the number. Then they destroy the pieces of paper. Then that number is entered into a calculator and eachperson subtracts their SSN and hands it to the next person to do the same. After all 3 have done this the remaining number is divided by 3.

Or they could just call payroll and ask someone their to average their 3 salaries for them.