One Key.
Three Boxes.
The key is in exactly one box. Only one of the following statements is true.
“The key is in B.”
“The key is not in B.”
“The key is not in A.”
Which box holds the key?
Take a moment to decide. Remember: only one statement can be true.
Need a Hint?
Compare A’s statement with B’s. Can both be true? Can both be false?
Reveal Answer & Explanation
The key is in Box A.
A and B contradict each other. The key is either in B or it is not in B. Exactly one of those two statements must be true.
That accounts for the only true statement. Because the puzzle permits just one true statement in total, C’s statement must be false.
Reverse C’s false statement. C says, “The key is not in A.” If that is false, the key must be in A.
Check the answer
With the key in Box A:
| Box | Statement | Result |
|---|---|---|
| A | The key is in B. | False |
| B | The key is not in B. | True |
| C | The key is not in A. | False |
Exactly one true statement. Both puzzle conditions are satisfied.
Challenge a friend
Can they solve it too? Share the puzzle without giving away the answer.