Case 117
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.
Avery
“Either Frankie or Jules is guilty.”
Jordan
“Avery is innocent.”
Frankie
“Either Avery or Logan is guilty.”
Logan
“Avery and Jordan are both innocent.”
Jules
“Jordan and Logan are both innocent.”
Who is guilty?
Solution: Frankie
If Frankie is guilty, Frankie's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.