Case 078
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.
Cameron
“Either Avery or Finley is guilty.”
Rowan
“Avery and Noah are both innocent.”
Avery
“Cameron and Noah are both innocent.”
Noah
“Cameron and Avery are both innocent.”
Finley
“Either Avery or Noah is guilty.”
Who is guilty?
Solution: Finley
If Finley is guilty, Finley's statement is false and every other statement is true. Testing the other suspects creates at least one contradiction.