1. Bob tells the truth on only one day of the week.
2. One day he said: "I lie on Mondays and Tuesdays."
3. The next day he said: "Today is either Thursday, Saturday, or Sunday."
4. The next day he said: "I lie on Wednesdays and Fridays."

On which day of the week does Bob tell the truth?

I am thinking.
Aha.
Days A and C are not both lying days because of the important fact.
We call this fact the other important fact.
I have proven that Day B is either Monday,Tuesday,Wednesday,or Friday.
Suppose it is a Friday.
Then,Days A and C are Thursday and Saturday,both lying days,contradictory to the super important fact.
Day B is either Monday,Tuesday,or Wednesday.

Posted by Tim Axoy on 2003-03-23 04:14:05