how intelligent are you ??[geniuses only]?

Question

3 geniuses are looking for jobs. they go for this inteview & they all pass ! the inteviewer [a super intelligent man decides to give them an ultimate test. he blind folds them & tells them he is putting paint on their foreheads either white paint or black paint. he says if you see black paint on someone stand up - if you know the colour on your forehead raise your hand.

when the blindfolds were removed all 3 stood up

after some moments one guy raises his hand and says the correct colour on his head . what was it & how did he know ?
[ I'm interested in the reasoning]

Answer 1

The colour was black. Since all three of them stood up, a minimum 2 will have black paint on their head. Out of 3, if only one person has black paint, then only 2 will see it. As the mentioned person knew which colour was painted on his forehead, he will only know that if one of the other 2 has white paint which means he has black.

Answer 2

I am no genius but I do find a possible answer here:

Let the geniuses be E, F and G.
If E had black then both F and G might stand.
E would only stand if either of the two: F / G had black.
So F / G had black.
Now F could also stand if G / E had balck.
Now G could also stand if F / E had black.

Being 'E' I might aasume he knew what F and G had.
So if F had BLACK and G had WHITE:
1. E must have BLACK.
Now the problem lies here:
2. If F had BLACK and G had BLACK
(a) and E had WHITE
(b) and E had BLACK
all 3 would still stand up.

However, if E had WHITE, either F or G would have come to the conclusion in 1. Since neither raised their hands, all MUST have BLACK.

So E had BLACK.

2nd : If 2 had BLACK and one WHITE it loses the WHITE guy as the other two would know instantly they have BLACK. It provides and unfair dis-advantage to the WHITE guy.

Answer 3

OBVIOUSLY The answer is the color on the guy who rose his hand had BLACK PAINT. This is because the guy with white paint saw two people with black paint. The two other guys see one other person with black paint, and only one person with white paint. And at least one person had to have White paint, so the Guy figured it was him with the white paint...does that even make sense by the way I explained it? Well like for instance

The all stand up

One guy sees that the other two people have black paint, so he figures he has white paint.

Each person with black paint saw the other guy who had black paint.

Each person must have saw that someone else had a black forehead and it was only important for there to be two blacks in order for everyone to see it. Unless everyne had black...

And if that's not it maybe the paint dripped onto the floor, or maybe it's because black paint smells weird...or there could be mirrors. Or maybe it's because black paint dries faster and the guy's forehead still felt wet. Or maybe they all have black foreheads.

Or maybe the guy who put the paint on them put paint on himself...nevermind

Okay, my final answer is that the black apint dried up quicker then whtie paint, or was it the other way around...i'm pretty confused now.

Answer 4

Duh...it is 3 Blacks.
1) When all 3 stood up, it was either 2B +1W or 3B.
2) After some moments, when no one raises their hand, it means no one saw White so the guy who raise his hand knew it was 3Blacks (3B).
Now since a few other people here have already answered correctly, the question is how do you (the questioner/interviewer :) ) pick the best answer or separate the wheat from the chaff?
Well, you have to ask the important next question
"Why would it NOT work if it was 2Blacks and 1 White on their foreheads?".
Now if they don't answer this 2nd question, you know they are not reading and not competing for the best answer (i.e. the job) and you will have to pick me as best answer 'cos I asked the 2nd important question. If they answer this 2nd question, I will pick the best answer for you but if there is no best answer, you have to pick me as best answer :).

Answer 5

Black paint

all 3 stood up because they could all see black paint, the correct man saw one with white and one with black paint, as the man with black paint cannot see his own forehead he must be seeing the black paint on the correct man's forehead.

I am not a genius.

The one with white paint would have no idea of knowing however so it was not a fair test by the interviewer.

Answer 6

the interviewer told the truth (that he used two colors), else there wouldn't be a solution to this problem.

since all stood up, two of them had black paint.

assume A and B had black and C had white.


either A or B could've raised his hand.

assume A raised his hand
since they all stood up, they all saw at least one of them with black paint. the person who raised his hand (A) knew that he had black paint because the other person with black paint (B) wouldn''t have stood up if he(A) had white paint since (C) had white paint.


(A and B are interchangeable)

Answer 7

If all three stood up it means at least two of them had black paint.
take condition 1. if only two had black paint and one had white then both the ones with the black paint would know that they had black paint on their foreheads.
condition 2. if all had black paint then no one would raise their hand because they would see two blacks but the most intelligent of them all would understand that no one is raising their hands because they are seeinf two blacks would immediately know that he has black paint on his forehead and would raise his hand.

Answer 8

Trick question.
It's not possible to tell.
The interviewer never said that both colors would necessarily be used.
Also, since there were three guys, as long as at least two of them had black paint, they could all stand up (because if they saw black paint on either of the other two guys' foreheads, they had to stand up).
So it's possible that one guy had white, but all three of them may have had black paint, so it's impossible to tell.

Answer 9

All they have to do to entitle them to stand is see a person with black. Yes there are two of them with black, and one who has white. But going on the basis that both colours were used, any one of them could have figured it out...
Person A = White
Person B = Black
Person C = Black
Person A stands up because he sees B, and C.
Person B stands up because he sees C.
Person C stands up because he sees B.
Any one of them could come to the realization that there has to be two with black and one with white,because they all are standing. A simple look at what the other two have would indicate what themselves have. It was a matter of the quickest brain, and a fair way to choose who to hire.
CyberNara

Answer 10

black. call the guy who answered A, and the other two B and C. if they all stood up, they all saw black paint. at least one of them had to have white paint, or there wouldn't be a solution. at least two of them had to have black paint, or the one with black would have seen only white and wouldn't have stood. so there are two blacks and one white. if he'd had the white paint, then he would have been no way of knowing it. if he had black paint, then the man (B) with white would have seen two with black and stood, and the last man (C), the other with black, would have seen A and stood.