Cards problem...

[psuresh1982]

My Friend has 3 cards face down on a desk. One is a queen and other two are kings. He knows which card has queen and king. You can ask my friend one YES or NO question, but when you do, you need to point to one of the cards. If you point to an king, he will tell the truth, if you point to the queen, he will randomly say YES or NO. You have to find one of the kings.

Tell me what question you need to ask my friend?

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suresh

[raj1402]

i think u can point to any card and ask

this is the one of the three kings

the answer should be no as only two kings are there

if he says no he is telling truth and the card is queen other two cards are knig

if he says yes he is telling lie and the card is queen other cards are king!!!

i think i got it correct!!!

[psuresh1982]

No raj. Your answer was wrong. For example you point the king card and ask my friend "this is the one of the three kings". So my friend answer is NO. According to your solution "if he says no he is telling truth and the card is queen other two cards are knig". Is it correct? plz work out all the possibilities.

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suresh

[raj1402]

If he says no he is telling the truth so the card is queen and other two cards are king
you can tell the other two cards are king right
we can find the cards which are king
if he says yes he is not telling the truth and the card is queen
this holds true when you point on queen suppose you point on king and ask the question he cant answer yes or no ...

[psuresh1982]

I think you didn't understand what i am saying...How you assume if he tell yes that card is queen.

Look at my question. "If you point to an king, he will tell the truth, if you point to the queen, he will randomly say YES or NO"

Also according to my previous post initially i am pointing the king card but your answer "that card is queen". Is it correct?

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suresh

[sopova123]

There can be only three arrangements of the card case 1:q k k case 2:k q k case 3:k k q the question we can ask by pointing to the first card, ie. The left most one is: "the card next to it is a queen" case 1 : a)he replies yes, which will be false , so third one is the king b)he replies no, which is true, so so second is king. Case 2: he will always reply yes as this is a king , then third will be automatically the king case 3: he will always reply no as this is a king , then second will be automatically the king to summarize: if he answers yes to the question, the third one will be a king if he answers no to the question, the second one will be a king.

[sopova123]

There can be only three arrangements of the card
Case 1:q k k
Case 2:k q k
Case 3:k k q
The question we can ask by pointing to the first card, ie. The left most one is: "the card next to it is a queen"

Case 1 : a)he replies yes, which will be false , so third one is the king b)he replies no, which is true, so so second is king.

Case 2: he will always reply yes as this is a king , then third will be automatically the king

Case 3: he will always reply no as this is a king , then second will be automatically the king

To summarize: if he answers yes to the question, the third one will be a king if he answers no to the question, the second one will be a king.

[psuresh1982]

Nice solution sopova123. Here is my answer for this question.....

Point to the middle card and say, "Is the card to the right an king?" If the answer is yes, then the card on the right is an king. If the answer is no, the card on the left is an king.

This solution works because if you're pointing to an king then he's obviously telling the truth and if you're pointing to the queen the answer doesn't matter anyway because you will pick one of the other two which are both kings.


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suresh

[raj1402]

im not clear if the middle card ur pointing is queen and

u ask is the card right to this is king he may tell yes or no as the card is queen!!!

then how to guess!!!

[psuresh1982]

Hi Raj,

Please read my question carefully.

My Friend has 3 cards face down on a desk. One is a queen and other two are kings. He knows which card has queen and king. You can ask my friend one YES or NO question, but when you do, you need to point to one of the cards. If you point to an king, he will tell the truth, if you point to the queen, he will randomly say YES or NO. You have to find one of the kings..

So if you point the queen then automatically you will find one of kings. Because both the side you have a king.

So my question is to find any one of the king not both. I think now you will clear.

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suresh

[raj1402]

[i]Point to the middle card and say, "Is the card to the right an king?" If the answer is yes, then the card on the right is an king. If the answer is no, the card on the left is an king. [i]

but

assume the centre card is queen and u r pointing to it and asking
" Is the card to the right an king?"

as the card u pointing is queen he may say the truth or lie

suppose he lies then

[psuresh1982]

Please complete your question......

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suresh

[raj1402]

assume the centre card is queen (u dont know that its queen)

and u r pointing to it and asking

" Is the card to the right an king?"

as the card u pointing is queen he may say the truth or lie

suppose he lies then how will u decide

just reply for this situation alone!!!

[psuresh1982]

Only one logic i am using here. If he says yes then i will take the right side card and if he says no then i will take the left side card. I never mind it is queen or king.

Situation 1: Card is Queen
Let we assume he tell truth. So he say YES and i will select the right side card as king. Let we assume he tell lie. So he say NO and i will select the left side card as king.

In the both assumption i will get the king card. Becasue both side of the queen we have a king.

Situation 2: Card is King
Here he tell truth. So he say YES if the king card as right and i will select that card. he say NO if the king card as left and i will select that card.

Still you doesn't understand please workout practically. Because i can't able to explain other than simply this. Or our geekinterview members will helps you.

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suresh