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Truth, lie or both

Truth, lie or both

There are people who answer everything with the truth, others who always lie, and others who alternate the truth with the lie so that if they answer a question with the truth the next answer will be a lie and vice versa. How could one find out, with only two questions whose answer is YES or NO, if a person is sincere, a liar, or if he alternates truths with lies?

Solution

You have to ask the person twice: Do you alternate the truth with lies?

Two negative answers show that she is sincere, two affirmative answers indicate that she is a liar and an affirmative answer and another negative one indicate that it is a person who alternates the truth with the lie.