Brain Teasers Open to All

  • #1
18,490
8,341
Unfortunately I don't have time to regularly post new brain teasers, I'm sure most have you have noticed :biggrin: So this means I am opening the forum to all. If you have a brain teaser you want members to try out, be my guest and post it! Please keep all threads solely brain teasers and not a general question or comment. Have fun!

Oh and marcus if you want to claim your prize, PM me :smile:
 

Answers and Replies

  • #2
123
0
Oh, sounds fun
 
  • #3
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Coloures Hats

Greg Bernhardt said:
Unfortunately I don't have time to regularly post new brain teasers, I'm sure most have you have noticed :biggrin: So this means I am opening the forum to all. If you have a brain teaser you want members to try out, be my guest and post it! Please keep all threads solely brain teasers and not a general question or comment. Have fun!

Oh and marcus if you want to claim your prize, PM me :smile:


Coloured Hats.

We have a box in which there are 2 white and 3 blue hats.
The light is turned out and 3 boys take at random one hat each and places it on his head.
The light is turned on again.
Each boy can see the colour of the hat of each of his colleages but not his own.
The first boy is asked the colour of the hat he is wearing.
He thinks and says he does not know.
The second boy is asked the colour of his hat.
He thinks and says he does not know.
The third boy is now asked and he replies Blue.
What was the reasoning of the third boy's answer?

I believe the logic will also work for red and green hats.
 
  • #4
Njorl
Science Advisor
267
13
I put it in white. Select to see:

Boy 1 did not see 2 white hats, or he would say his hat was blue.

Boy 2 knows that boy 1 saw at least 1 blue hat. If he sees a white hat on boy 3, he knows his own hat is blue. He does not see a white hat there.

Boy three knows boy 2 saw a blue hat on him. He knows his own hat is blue without even seeing the other boy's hats.



NJorl
 
  • #5
Gokul43201
Staff Emeritus
Science Advisor
Gold Member
7,083
18
Njorl, Darn you man !

For the longest time, I misread your first line - I read the line without the "it". So I thought you guessed "white". So, I rechecked my solution a gazillion times before I gave up and went through your's - only to find that you went on to finally "contradict your opening line" - or at least, as I had read it.

Why are puzzles being posted on the sticky ? And why don't people come back to say if you're right or wrong ?
 
  • #6
644
1
Quote:
"i put it in white"

to be read as i put the solution in white :p :D

Quote:
"Why are puzzles being posted on the sticky ? And why don't people come back to say if you're right or wrong ?"

Probably they never expected anyone to solve it ?? :P :D
 
  • #7
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the first two boys are wearing white hats and there are only two white hats, so what the third boy picked was one of the three blue hats
 
  • #8
31
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Thanks for the replies.
The third boy was not wearing a white hat, because had this been the case the second boy could have said blue because the first boy was unable to say blue because he did not see two white hats.
Whats a sticky anyway.
 
  • #9
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
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Ian Rumsey said:
Whats a sticky anyway.

I will put the answer in white:

a "sticky" is a sticky thread
a sticky thread is a thread that stays at the top of the list of threads.
"mentors" i.e. moderators have the power to create stickies
Normal threads are sorted by date (usually most recent post) and so
the more active threads stay high in the listing and are the easiest to find.
However there may be some threads containing useful or important information that the mentor wants to remain always readily availble

Select to see.
 
  • #10
I have a good solution I think:


If 1 saw 2-blue, 3-blue; 1 could be 1-blue or 1-white.

If 1 saw 2-white, 3-blue; 1 could be 1-blue or 1-white

If 1 saw 2-blue, 3-white; 1 could be 1-blue or 1-white.

If 1 saw 2-white, 3-white; 1 would know he's blue by default. But he didn't.



If 2 saw 1-blue, 3-blue; 2 could be 2-blue or 2-white.

If 2 saw 1-blue, 3-white; 2 could be 2-blue or 2-white.

If 2 saw 1-white, 3-blue; 2 could be 2-blue or 2-white.

If 2 saw 1-white, 3-white; 2 would know he's blue by default. But he didn't.


If 3 saw 1-blue, 2-blue; 3 could be 3-blue or 3-white.

If 3 saw 1-blue, 2-white; 3 must be blue, or else 1 would have known. But he didn't.

If 3 saw 1-white, 2-blue; 3 must be blue, or else 2 would have known. But he didn't.

Conclusion: 3 must be blue, or else 1 and 2 would have already been able to determine their own hat colors, but they weren't able to.


I hope this is clear. I decided to write it out somewhat logically instead of in long sentences, I hope it helps.
 
  • #11
NateTG
Science Advisor
Homework Helper
2,450
6
I'm not an admin, but

Please put puzzles in threads rather than here.
 
  • #13
6
0
Not quite a puzzle

A cheeky boy was digging a hole in the garden.

An elderly neighbour overlooking him across the fencing and asked,
"What are you doing there kid"

The kid replied without looking up, "My goldfish has died, and I am burying it here"

That old man continued, "That's an awfully big hole for a gold fish!".


Guess what did the kid reply.
 
  • #14
516
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The goldfish died by being flushed down into the sewage tank... the boy has to get the goldfish before he can bury it...
 
  • #15
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Michael66 said:
A cheeky boy was digging a hole in the garden.

An elderly neighbour overlooking him across the fencing and asked,
"What are you doing there kid"

The kid replied without looking up, "My goldfish has died, and I am burying it here"

That old man continued, "That's an awfully big hole for a gold fish!".


Guess what did the kid reply.

it was a big goldfish
 
  • #16
JamesU
Gold Member
766
3
I think... he wanted to get it out of the sewer. :rofl:
 
  • #17
1,031
16
Answer (whited out) His father had eaten the goldfish
 
  • #18
It's for the cat that ate the goldfish.
 
  • #19
1,550
0
New white out code

White out New white out code

(color=#black) New white out code (/color)
use [ not (
 
  • #20
479
2
This is good to have, but usually what's good about a white out is that there's some indication that there is something there. However, there's a difference between "whited-out" and "invisible," but we'll see how it works out. Maybe there can be better indication that there actually is something whited out and exactly where it is by putting it in parentheses or something. Otherwise, they'll be overlooked.
 
  • #21
Mk
2,001
3
Michael66 said:
That old man continued, "That's an awfully big hole for a gold fish!".

Guess what did the kid reply.
My goldfish lives in China.
 
  • #22
Michael66 said:
A cheeky boy was digging a hole in the garden.

An elderly neighbour overlooking him across the fencing and asked,
"What are you doing there kid"

The kid replied without looking up, "My goldfish has died, and I am burying it here"

That old man continued, "That's an awfully big hole for a gold fish!".


Guess what did the kid reply.

Oh it's not just for the fish, it's for nozy neigbours too.:smile:
 
  • #23
388
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I don t know what qualify as a puzzle. I like to think about physics, and math problems.
 
  • #24
2
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Each boy can see the colour of the hat of each of his colleages but not his own.
Yeah but I think the point is that the boys were ligned so that the third one saw the hats of the other two in fron of him, the second only of the one in front of him and the last one saw no hats at all and yet he guessed the answer.
.
^^ u proved that the one that guessed his color could have done that by not looking at the hats at of colleages at all .
 
  • #25
Gib Z
Homework Helper
3,346
6
My goldfish lives in China.

For the longest time i was thinking you were describing China as a hole and was laughing at that :D Only now i realise you were referring to its location on the other side of the world :)
 

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