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 True Day (Posted on 2003-03-17)
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?

 See The Solution Submitted by ET Rating: 4.1667 (6 votes)

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 re: Confusion | Comment 6 of 10 |
(In reply to Confusion by Alan)

But if on sunday he said he lied on mondays OR tuesdays, then that would not be a lie, as he does indeed lie on mondays. It is only because he says he lies on both mondays AND tuesdays that telling the truth on tuesday alone makes it a lie. Remember de Morgan's laws: not(A AND B) = (not A) OR (not B) and the similar not(A OR B) = (not A) AND (not B). And the other way of looking at it, the ANDed statement is one statement, not two.
 Posted by Charlie on 2003-03-17 17:09:11

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