Latest Infosys Aptitude Question SOLUTION: The puzzle is Nine IIT students were sitting in a classroom. Their professor wanted them to test. Next day the professor told all of his 9 students that he has 9 hats, The hats eit

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(#M40010600) INFOSYS question Keep an EYE

The puzzle is Nine IIT students were sitting in a classroom. Their professor wanted them to test. Next day the professor told all of his 9 students that he has 9 hats, The hats either red or black color. He also added that he has at least one hat with red color and the no. of black hats is greater than the no. of red hats. The professor keeps those hats on their heads and ask them tell me how many red and black hats the professor have? Obviously students can not talk to each other or no written communication, or looking into each other eyes; no such stupid options and no tricks.
Professor goes out and comes back after 20 minutes but nobody was able to answer the question. So he gave them 10 more minuets but the result was the same. So he decides to give them final 5 minutes. When he comes everybody was able to answer him correctly.

So what is the answer? and why?

Asked In Infosys alluri udaykumar (11 years ago)

Solved PARAG KAMRA Read Solution (11)

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Read Solution (11) :

PARAG KAMRA  (11 years ago)

After 20 minutes :
Lets assume that their is 1 hat of red color and 8 hats of black color. The student with red hat on his head can see all 8 black hats, so he knows that he must be wearing a red hat.
Now we know that after first interval nobody was able to answer the prof that means our assumption is wrong. So there can not be 1 red and 8 black hats.

After second interval of 10 minutes :
Assume that their are 2 hats of red color and 7 hats of black color. The students with red hat on their head can see all 7 black hats and 1 red hat, so they know that they must be wearing a red hat.
Now we know that after second interval nobody was able to answer the prof that means our assumption is again wrong. So there can not be 2 red and 7 black hats.

After third interval of final 5 minutes :
Now assume that their is 3 hats of red color and 6 hats of black color. The students with red hat on their head can see all 6 black hats and 2 red hats, so they know that they must be wearing a red hat.
Now we know that this time everybody was able to answer the prof that means our assumption is right.

So there are 3 red hats and 6 black hats.

Now as everybody gave the answer so there can be a doubt that only those 3 students know about it how everybody came to know ?
Then here is what i think, the professor gave them FINAL 5 minutes to answer, so other guys will think that the professor expects the answer after 3rd interval (according to prof it must be solved after 3 intervals), so this is the clue for others.

Is this solution Helpfull? Yes (17) | No (13)  

piyushkumar  (11 years ago)

Parag i didnt get you.. because why didnt you take 1 red and 8 blue hat as your first assumption..

Is this solution Helpfull? Yes (5) | No (2)  

Garima  (11 years ago)

3 red hats and 6 black hats.

I shall give the logic later, (if correct) .

Let others think.

Is this solution Helpfull? Yes (4) | No (6)  

Garima  (11 years ago)

I think, Logic given by Prag is correct.

Is this solution Helpfull? Yes (1) | No (4)  

malathy  (11 years ago)

5 bcoz he gave the clue that he will give 5 more min.

Is this solution Helpfull? Yes (1) | No (5)  

nishu jindal  (11 years ago)

i didn't get parag soln.
as we knw tht there is 1 red color hat then after 1st interval we get the soln tht 8 black n i red..... i didn't get answer

Is this solution Helpfull? Yes | No (3)  

Amod Kumar Lal  (11 years ago)

Parag your answering logic is wrong. You did notice that at the 3rd interval everyone get to know the answer, but in ur case only 3 students know the answer.

Is this solution Helpfull? Yes | No (1)  

Ravi.Bhagya Sri  (11 years ago)

It is not given that the student with the red hat is able to see the students with black hats. Then how can u say that the student with red hat is able to see the black ones?

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neelimamalineni  (10 years ago)

can anyone explain me

Is this solution Helpfull? Yes | No (2)  

malliakrjuna  (8 years ago)

given he had at least one hat with red color out of 10 hats. so probably there is one red hat and 9 black hats

Is this solution Helpfull? Yes | No (1)  

Abhilash Kumar  (7 years ago)

Thereshould be one red hat.may be more than one .suppose igot one hat ,obviously after the first break ican say one red and remaining are blacks.and all too.
Because that is the only answer every one can say undoubtly.after the first intervel every body understood that red hats are more than one.
So the next option is 2red hats and 7 blacks.after the second break every body answering likethat.but professor not agreed for that.the next option is 3 red and 6 blacks
After the third intervel everybody said the same .this was right right numbers.so every body answered correctly.
So the answer is 3 red and 6 black hats

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