Four people of Taro, Jiro, Hanako, Fujiko are a honest person or a liar respectively.
Taro said, "There are three liars among us."
Jiro said, "There are three or more liars among us."
How many honest persons are there among four persons ?
Taro said, "There are three liars among us."
Jiro said, "There are three or more liars among us."
How many honest persons are there among four persons ?
Answer
Supposing the number of liar is four, since the utterance of Jiro becomes true, the number of liar is not four.
Since the utterance of Taro and Jiro will become true supposing the number of liar is three, the number of liar is not three.
Supposing the number of liar is two, Taro and Jiro should be honest, Hanako and Fujiko are liar, which is OK.
Supposing the number of liar is one, the talk of Taro and Jiro becomes a lie, and Taro and Jiro are liar which is contradictory to assumption.
Two persons
Solution
Because both of Taro and Jiro tell the number of liar, you should consider the number of liar in order.
Supposing the number of liar is four, since the utterance of Jiro becomes true, the number of liar is not four.
Since the utterance of Taro and Jiro will become true supposing the number of liar is three, the number of liar is not three.
Supposing the number of liar is two, Taro and Jiro should be honest, Hanako and Fujiko are liar, which is OK.
Supposing the number of liar is one, the talk of Taro and Jiro becomes a lie, and Taro and Jiro are liar which is contradictory to assumption.
