Fog Creek Software
Discussion Board

A Queen's decree

Hope y'all like this one:

Friday, May 3, 2002

If there were one unfaithful husband, his wife would realize immediately, seeing as she knew of none and there had to be one, and would kill him the first night.
If there were 2 unfaithful husbands, their wives would each know of one unfaithful husband. When he didn't get killed on the first night, they would both conclude that their husband was unfaithful, and kill him on the second night.
Following this process, we can see that 40 husbands died on the fortieth night.

Paul Viney

Paul Viney
Saturday, May 4, 2002

I have seen similar problems before, and I must say the reasoning expected makes me kind of uneasy. Look at it this way. A woman knows 39 other adulterous men. She does not know that her husband is adulterous. But we expect her to think 'Day one gone. So the answer is not 1. Day 2 gone. So the answer is not 2....' till 'day 39 gone. Hey it must be my husband!'. I understand the logic. I just cannot see myself thinking like that if I were that woman.

Thursday, May 9, 2002

While I agree with your point, Ravikiran, I feel that a women who instinctively knows about all other unfaithful husbands on the island, and who is prepared to shoot her husband after just thinking about the problem is obviously capable of anything.

Paul Viney

Paul Viney
Thursday, May 9, 2002

I've seen this problem told in a lot of different ways.  The coolest description of this problem I've seen is in the book "Labyrinths of Reason" by William Poundstone.  In that one, the "women" are extremely paranoid employees of a merging mega-corporation, who live in constant fear of losing their jobs.
It's a really neat problem.  The reason the solution seems less than satisfying is that it rests on the assumption that all the women are perfectly logical.  If even one woman makes the slightest error in their deductive reasoning, the solution falls apart, and you end up with quite a lot of dead husbands!

Billy Martin
Saturday, May 18, 2002

*  Recent Topics

*  Fog Creek Home