Yet another brain teaser, now with solution

[achris]

This is a really good one and doesn't require a calculator. You could use one, but it ain't gonna help...

"A wealth father has 3 quite intelligent sons. He decides to conduct a test to see which one is the smartest, and they will inherit the family fortune.

He puts them in a dark room, facing each other, with instructions that no-one is to say anything. He tells them that he will put either a red spot or a white spot on their foreheads. If any boy sees two reds he must clap his hands. The first boy to deduce his own colour is the winner, and hence inherits the family fortune. The light goes on, no-one says anything and no-one claps. A few seconds later the oldest boy (of course) says he knows his own colour.

The questions to you, my fellow iBoaters is: What was his colour and how did he figure it out?

Chris.............
PS. There are no mirrors in the room and none of the boys wears glasses or has anything reflective, and the windows are covered by curtains (drapes). And none of the boys used sign language of any sort. I think I've covered everything...

 

[Hoss the Hermit]

Re: Yet another brain teaser

Re: Yet another brain teaser

White. One of the others had a red one. If his was red, the third one would have clapped

 

[achris]

Re: Yet another brain teaser

Re: Yet another brain teaser

White is correct, but your rationale is flawed...
Please try again...

Chris............

 

[SgtMaj]

Re: Yet another brain teaser

Re: Yet another brain teaser

I thought his rationale made perfect sense unless none of the other two had red ones.

On that note...

White, because he was color-blind and wasn't given any instructions about gray dots.

White, because one of the others had a red dot, and the other didn't have a dot at all, so he realized his father only issued A red one and A white one.

White, because he's not hindu.

 

[achris]

Re: Yet another brain teaser

Re: Yet another brain teaser

I thought his rationale made perfect sense unless none of the other two had red ones.

On that note...

White, because he was color-blind and wasn't given any instructions about gray dots.

White, because one of the others had a red dot, and the other didn't have a dot at all, so he realized his father only issued A red one and A white one.

White, because he's not hindu.

Now you're just being silly!!!

ok.. all had white dots, no-one was colour-blind. The 'one red dot' rationale was wrong because if any one of the boys saw one red and one white and didn't hear a clap he would know immediately that his was not red. Remember, the oldest boys waited a few seconds.... and I did say they were all quite intelligent.

Take all the fun out of it when you have to explain it...

Chris................

 

[Turin]

Re: Yet another brain teaser

Re: Yet another brain teaser

Ha! My girlfriends guess was 'all had white dots' and i thought the oldest one must have a red dot. I guess she's smarter than me (at least, this time )

 

[Hoss the Hermit]

Re: Yet another brain teaser

Re: Yet another brain teaser

Now you're just being silly!!!

ok.. all had white dots, no-one was colour-blind. The 'one red dot' rationale was wrong because if any one of the boys saw one red and one white and didn't hear a clap he would know immediately that his was not red. Remember, the oldest boys waited a few seconds.... and I did say they were all quite intelligent.

Take all the fun out of it when you have to explain it...

Chris................

Gettin' it right is all that matters, don't matter the rationale. "think outside the box". If ya shoot the bad guy instead of the good guy, it doesn't matter how ya knew which was which, it matters that you're alive.

 

[SgtMaj]

Re: Yet another brain teaser

Re: Yet another brain teaser

I wanna know how he figured it out...

 

[achris]

Re: Yet another brain teaser

Re: Yet another brain teaser

I wanna know how he figured it out...

That, my friend, is the puzzle. Besides, I've given you half of it already...

 

[achris]

Re: Yet another brain teaser, now with solution

The solution to this puzzle is quite simple, but in order to work it out you have to 'work the negatives'. Work out why a particular solution won't work.

So, that said....

All three had white dots....

The way the oldest boy worked is was.. He saw 2 whites.. If he had a red then both of the other boys would have seen red-white and not known their own colour... Each of them would also be aware that if his own colour was red there would have been a clap. No clap=only one red, therefore his was white. So there would have been almost no delay and one of the other boys would have known his own colour. So, the eldest boy deduced, because of the delay there was no red dot anywhere. Ergo, his was white.... Each boy, being 'quite intelligent' would have reached the same conclusion at about the same time, it was just that the eldest was just that bit quicker.

Hope that's clear...

Chris..............

 

[SgtMaj]

Re: Yet another brain teaser, now with solution

makes sense NOW...

I still liked Hoss' answer, since you didn't clarify that all had white dots until after he answered...

 

[achris]

Re: Yet another brain teaser, now with solution

.... you didn't clarify that all had white dots until after he answered...

I didn't need to... If you re-read the solution you'll see that if a red dot was present then one of the boys would have known his own colour almost immediately.

C....

 

[SgtMaj]

Re: Yet another brain teaser, now with solution

Right, and "a few seconds" is almost immediately.