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Prince Puzzle: Newsletter Challenge (May 2020)

Posted April 30, 2020 5:01 PM
Pathfinder Tags: challenge question princes

This month's IEEE GlobalSpec Newsletter Challenge is:

A king wants his daughter to marry the smartest of three intelligent young princes, and so the king's wise men devised an intelligence test.

The princes are gathered into a room and seated, facing one another, and are shown two black hats and three white hats. They are blindfolded, and one hat is placed on each of their heads, with the remaining hats hidden in a different room.

The king tells them that the first prince to deduce the color of his hat without removing it or looking at it will marry his daughter. A wrong guess will mean banishment from the kingdom. The blindfolds are then removed.

You are one of the princes. You see two white hats on the other prince's heads. After some time you realize that the other prince's are unable to deduce the color of their hat, or are unwilling to guess. What color is your hat?

(Note: Assume that your competitors are very intelligent and want nothing more than to marry the princess. Also assume that the king is a man of his word, and he has said that the test is a fair test of intelligence and bravery.)

And the answer is:

The king would not select two white hats and one black hat. This would mean two princes would see one black hat and one white hat. You would be at a disadvantage if you were the only prince wearing a black hat.

If you were wearing the black hat, it would not take long for one of the other princes to deduce he was wearing a white hat.

If an intelligent prince saw a white hat and a black hat, he would eventually realize that the king would never select two black hats and one white hat. Any prince seeing two black hats would instantly know he was wearing a white hat. Therefore if a prince can see one black hat, he can work out he is wearing white.

Therefore the only fair test is for all three princes to be wearing white hats. After waiting some time just to be sure, you can safely assert you are wearing a white hat.

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#1

Re: Prince Puzzle: Newsletter Challenge (May 2020)

04/30/2020 8:55 PM

If you see white-white than the others must see white-white or white-black.

If either of the others sees white-black then they should know their own hat is white. If their own hat were black, the other one would know right away his hat was white. (There are only 2 black hats.) So each of the others sees white-white.

Therefore, you know your hat is white and you are quicker than your competitors.

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#2
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

04/30/2020 10:38 PM

Congratulations !!! You Win....

Haha...not so smart now, are ya'...

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#5
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/01/2020 11:17 AM

...The blindfolds are then removed...

Please, could I have my blindfold back?

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#6
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/01/2020 3:07 PM

You got the nice one....her sister is the mean one....

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#9
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/02/2020 11:03 PM

That reminds me of Benjamin Franklin's essay on choosing an older mistress.

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#8
In reply to #1

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/02/2020 4:59 AM

GA.

It's also the only way to be a fair challenge (satisfying the note) - any other case would not create equal chances.

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#12
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/04/2020 5:42 AM

Good, but there is a nagging assumption in here: That you are necessarily smarter or faster, giving the answer first.

Why are the others incapable or unwilling (or slower) to give the answer?

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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/05/2020 12:33 PM

Why are the others incapable or unwilling (or slower) to give the answer?

The answer is they were in on the gag. I got fished in! #2

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#3

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/01/2020 12:44 AM

There are three different distributions of hats as seen by each individual.

  1. Two black hats, which leaved them with the answer they are wearing a white hat.
  2. A black and a white hat, if they are wearing a black hat, then one of the others would see two black hats, which is not the intension of the test, therefore they are wearing a white hat.
  3. Two white hats, If they are also wearing a white hat, then that also would be acting against the intensions of the test, therefore they are wearing black.
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#4
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/01/2020 1:13 AM

"After some time you realize that the other prince's are unable to deduce the colour of their hat, or are unwilling to guess. What colour is your hat?"

Did not take the above into account, that situation would come about if all three where wearing white hats, giving them the option of wearing either colour, therefore the answer is they are all wearing a white hat. Acting on there hesitation I answer WHITE.

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#7

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/02/2020 1:35 AM

Since the other two princes are in a quandary each must be wondering that the hat on his head could be black and hence kept quiet .

The only possibility in such a situation is that all three princes were wearing white hats , and since our Hero prince knew that, declares it and wins the princess in the bargain . All this , because the others did not answer ; they were not asked !

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#10

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/03/2020 12:03 AM

Black. If I had a white hat then one of the others would quickly guess black because they are two white hats but the fact they are both silent is that are a blak had and a white hat so it is fifty fifty. This.. I must have a black had.

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#11

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/03/2020 3:17 AM

This question must be in jest. Who would ever question a womans ability, but the father, who trained the daughter well enough to doubt her judgment to choose well.

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#13

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/04/2020 8:50 AM

Some questions have no black-and-white answers, though...

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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/04/2020 7:31 PM

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#16

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/12/2020 11:05 AM

There are 3 levels of intellectual complexity involved here. The first level is characterized by the thought that if you see 2 black hats, yours is white. The second level is characterized by the thought that if you see black and white, you must realize that because the other person with the white hat is obviously not seeing black and black (otherwise they would know first) therefore yours is white. The third level is characterized by the thought that if you see white and white, you then deduce that if the others saw white and black they would use the second level of intellectual complexity to deduce that their hat was white. Therefore since they aren’t, they are seeing white and white and therefore your hat is white. This is predicated on the assumption that the other 2 competitors are of equal intelligence, both in capacity and speed and that you are obviously superior to some extent in relation to capacity, speed or both. My observation however is that this is very likely not true, if I may understate my experience. (This is not a cut on anyone. Every person has different strengths and weaknesses in different areas, and even on different topics. I don’t consider myself to have superior intellect on any topic.) Any variance in intellectual capacity or speed throws this scenario off. One makes assumptions based on the level of intelligence of the other 2 (i.e. their ability to interpret data with the same skill and speed as the other). By definition if one wins the contest, the 3 do not have equal intelligence. Since abilities vary in the real world, anyone giving the first answer is giving it only on this inherently flawed assumption about the level of intelligence of the other 2 competitors, and therefore one could conclude that the first person giving the answer is potentially not as intelligent as the other 2, though that person is more brave, which was partly what the test was meant to discover. And if you are basing the answer “white” on the concept of perfect fairness, then if all 3 are of equal high intelligence, all 3 should have yelled out in unison “my hat is white” before they even put the hats on.

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#17
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Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/12/2020 11:43 AM

I went through the same inductive reasoning process, then realized it was like the prisoner's execution puzzle. The judge ordered the prisoner to be executed within the next seven days, then told the prisoner that he would not know when until the day when he would be executed.

In his cell, the prisoner reasoned thus: If I am still alive on Friday, I will be executed on Saturday, so I will know that day when I will be executed. Therefore Saturday is not the day I will die. That means it must be by Friday. But then if I am still alive on Thursday, I'll know it must be Friday, which would go against the judge's order, so Friday is out. Thus, using inductive reasoning to work backward from each day, he concluded that the judge's order was impossible to fulfill, so he could not be executed.

He was very surprised when they came for him on Tuesday.

This is similar to the problem of the one prince deciding whether his own hat is black or white based on the behavior of the other two princes. The only scenario that can definitely be ruled out is two black hats and one white; induction cannot be properly applied here, just as the prisoner could not correctly extend his argument beyond Saturday.

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#18

Re: Prince Puzzle: Newsletter Challenge (May 2020)

05/20/2020 9:33 AM

Answer is posted.

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