Are all of them innocent?
In a bus, David was found murdered. The bus driver called a detective. The detective found four suspicious people: Peter, Sara, Ken and Jennifer. The detective asked them, "Who is the murderer?" In reply, they make the following statements.
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Peter: "I'm innocent. Sara was talking to David."
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Sara: "I'm innocent. I did not speak to David."
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Ken: "I'm innocent. Jennifer killed him."
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Jennifer: "I'm innocent. One of the men killed him."
After a little time, the helper of the detective asked, "Isn't it an easy case for you?"
"Yes," answers the detective. "Four true statements and four false ones, piece of cake!''
Only one person is a murderer. Who murdered David?
Clarification: Peter and Ken are men. Sara and Jennifer are women.
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1 solution
Sara killed David. There are only four true statements. Only one person is guilty. Therefore, three of the "I'm innocent" statements are true. Only one more statement can be true, and this must be the one made by Peter or by Sara. Therefore, "The Jenifer killed him" and "One of the men killed him" are false statements, so the Sara is the killer.