brainteaser: one indian is bound on a stake. second indian

Question

brainteaser:

one indian is bound on a stake. second indian is bound with his back on the first indian. third indian is bound with his back on the front of the second indian. first indian sees second and third indian. second indian sees only third indian. third indian sees none of the indians behind him. there are two red ties and three white ties. each indian wears only one of these ties on his head. each indian is allowed to speak only when he knows the colour of his ties. then he is free. hence, they are not allowed to speak to each other.

third indian tells the colour of his tie and he is free.

what is the color of his tie ?

 :-D

kapslock · Answer

Is this a logical reasoning question or lateral thinking one? I can think of it in this way. The first Indian sees both the Indians before him wearing red, and he realizes that the red ties would have been exhausted (there're only 2 of them) and says "white" and is freed. Realizing that the first Indian is freed, the other two Indians would realize that their ties are red, and that's why the first said "white". So they say "red" and make their exit. Sounds palatable???

christoph · Answer

logic mixed with out-of-the-box-thinking :-)

third indian is the first one who speaks...

kapslock · Answer

Hmm, Christoph, you're not making things easier for me

I am feeling like Neils Bohr here (the long story would follow, if anyone's interested), but here goes the solutions (both the weird and not-so-weird ones

) Okay, another solution is (I didn't know the meaning of stake, till dictionary.com helped me out, and makes this solution also quite probable, though still out-of-the-box). The third Indian thought if he is going to be burnt anyway (the stake is a pole to which people are tied before being burnt), he just as well might take a risk. So he took a logical guess, thinking white is more than red, so greater chance of his own tie being a white than red. By chance it is correct, and he walks free. Another solution is that the third Indian thought that the first and second Indians are silent. The first can see both 2nd and mine ties, and yet is not speaking. Thus, 1. At the least one of 2nd and my ties is white. Now the second is not speaking too. What can he be scared of? If mine is red, then definitely his should be white, and he should speak up. Thus mine's not red. So mine's white. So he says white and walks free. 2. Both of ours ties are white. So he says "white" and walks free"

christoph · Answer

kapslock, you are on the right track :-)

1st indian is calm ! why ? because the 2nd and 3rd indian might wear white/white, red/white or white/red. he doesnt know. 2nd and 3rd indian know that not both of them wear red ties. 2nd indian is calm ! why ? because he sees that the 3rd indian wears a white tie. therefore he could wear a white or red tie. 3rd indian is not calm ! why ? because the others were calm. hence, he knows that he wears a white tie. who is niels boehr ?

kapslock · Answer

Christoph, I am putting this down (hoping the mods won't ban me for putting something out-of-context here).

Keep in mind, that this is most likely an urban legend ...

The following concerns a question in a physics degree exam at the University of Copenhagen:

"Describe how to determine the height of a skyscraper with a barometer."

One student replied:

"You tie a long piece of string to the neck of the barometer, then lower the barometer from the roof of the skyscraper to the ground. The length of the string plus the length of the barometer will equal the height of the building."

This highly original answer so incensed the examiner that the student was failed immediately. The student appealed on the grounds that his answer was indisputably correct, and the university appointed an independent arbiter to decide the case.

The arbiter judged that the answer was indeed correct, but did not display any noticeable knowledge of physics. To resolve the problem it was decided to call the student in and allow him six minutes in which to provide a verbal answer that showed at least a minimal familiarity with the basic principles of physics.

For five minutes the student sat in silence, forehead creased in thought. The arbiter reminded him that time was running out, to which the student replied that he had several extremely relevant answers, but couldn't make up his mind which to use. On being advised to hurry up the student replied as follows:

"Firstly, you could take the barometer up to the roof of the skyscraper, drop it over the edge, and measure the time it takes to reach the ground. The height of the building can then be worked out from the formula H = 0.5g x t squared. But bad luck on the barometer."

"Or if the sun is shining you could measure the height of the barometer, then set it on end and measure the length of its shadow. Then you measure the length of the skyscraper's shadow, and thereafter it is a simple matter of proportional arithmetic to work out the height of the skyscraper."

"But if you wanted to be highly scientific about it, you could tie a short piece of string to the barometer and swing it like a pendulum, first at ground level and then on the roof of the skyscraper. The height is worked out by the difference in the gravitational restoring force T =2 pi sqr root (l /g)."

"Or if the skyscraper has an outside emergency staircase, it would be easier to walk up it and mark off the height of the skyscraper in barometer lengths, then add them up."

"If you merely wanted to be boring and orthodox about it, of course, you could use the barometer to measure the air pressure on the roof of the skyscraper and on the ground, and convert the difference in millibars into feet to give the height of the building."

"But since we are constantly being exhorted to exercise independence of mind and apply scientific methods, undoubtedly the best way would be to knock on the janitor's door and say to him 'If you would like a nice new barometer, I will give you this one if you tell me the height of this skyscraper'."

The student was Niels Bohr, the only Dane to win the Nobel Prize for physics.

brainteaser: one indian is bound on a stake. second indian

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