Red faced children
A teacher tells a group of children that at least one of them has a red face. ‘Step forward if you have a red face’, he says at intervals, until... What happens next?
Assume that the children are clever enough to behave logically, they aren't disobedient and they can see each others faces, but not their own.
Assume that the children are clever enough to behave logically, they aren't disobedient and they can see each others faces, but not their own.
Labels: logic
posted by Chris at
12:06 PM
7 Comments:
They all step forward when see no one else is stepping forward. Then they all step backward when they deduce no one is redfaced.
Hi Ragknot. I'm sorry, but that's wrong.
This one is quite tricky. I'll give a clue, if only one child had a red face, then he would step forward on the first request.
They would all look to the child with the red face, and he would step forward, seeing that no other child has a red face.
Hi Sara, that's only an answer to the clue, not the main puzzle.
What would happen if there were 20 children and 5 had red faces?
Well, if there's only one, that child will step forward immediately.
If there are two, then those two will see only one other. Since that child does not step forward immediately then each will realize that he/she also has a red face and they will both step forward.
If there are three, then after a longer pause, all three will step forward.
There will be longer and longer pauses for each additional child with a red face.
So it all depoends on ehat assumptions you make about each child's reaction time.
Hi Wiz, you got it (no surprise there:). The reaction time was meant to be dealt with by the teacher pausing between his instructions - perhaps that could have been emphasized better in the posted problem.
Rajesh had posted a similar problem on 5 Oct 07 - "Infidelity Kills".
It's best to suspend disbelief when doing problems like this ^^
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