Case 196
The Swapped Envelope
A sealed envelope was replaced with an empty one.
Rule: exactly one suspect is guilty. The guilty suspect lies. Every innocent suspect tells the truth.
Finley
“Drew and Avery are both innocent.”
Harper
“Either Finley or Taylor is guilty.”
Drew
“Harper and Avery are both innocent.”
Avery
“Either Harper or Taylor is guilty.”
Taylor
“Finley is guilty.”
Who is guilty?
Solution: Taylor
If Taylor is guilty, Taylor's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.