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?

(In reply to I Got This !!!! by Ravi Raja)

Ravi, I think Charlie has the right answer.

Let's assume that the 'truth day' is Monday as you suggest.

This means: his first statement is False (as he doesn't lie on Mondays AND Tuesdays); his second statement must be False (since for it to be true his 'truth day' must be Thursday, Saturday or Sunday); and his third statement is True (since he tells the truth only on Mondays he must be lying on Wednesdays and Fridays).

In (a): the days you give aren't consecutive. If we assume that the first day is Tuesday, then the third day is Thursday, (not Friday). In either case since Bob's third statement is true then he tells the truth on Thursday (or Friday). But he only tells the truth on Mondays so this is inconsistent.

In (b): Bob gives the true statement on Saturday. But again he only gives the truth on Mondays so this is also inconsistent.

This had me tied up in knots for ages, and when I finally got the answer the hardest part was trying to explain it lucidly. Well done Charlie with the understandable explanation. Better luck next time Ravi.

Posted by fwaff on 2003-03-17 04:21:40