Case 175
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.
Sam
“Taylor and Parker are both innocent.”
Elliot
“Either Sam or Blake is guilty.”
Blake
“Either Elliot or Parker is guilty.”
Taylor
“Either Blake or Parker is guilty.”
Parker
“Elliot and Taylor are both innocent.”
Who is guilty?
Solution: Blake
If Blake is guilty, Blake's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.