Three women were seated around a table. After blindfolded, a numbered disc was pasted on each of their foreheads. The women were truthfully told "Each of you has either a 1, a 2 or a 3 on your forehead, and the sum of your numbers is either 6 or 7".
After the blindfolds were removed, each woman in turn was asked to name the number on her forehead without seeing it. The question was repeated until only one woman failed to name the number on her forehead.
When it was logically possible to name the number on her forehead, each woman did so; when it was not logically possible to name the number on her forehead, she would said "I donīt know my number", and waited until the question was repeated to her next time around.
Each woman had a 2 on her forehead. Which woman failed to name her number?
You seem to be missing the last step in my mind. When B and C know their answers is in round 2, then A will know her number must be a 2 in round 3.
If A's number was a 3, then C would has known her number (as 2) in the end of round 1. That is because if A would have seen a 1 on C, then she would have known her (as 3) right off the bat. So C would know she did not have a 1 making it impossible for A to have 3.
Try giving any of the three women a 1 or 3 and you will see how much more quickly they figue out what they have.
Re: An Answer (The correct one?)
