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Problem 823

AMC 12 late, AIME early
Combinatorics Difficulty 4.5 Multiple choice Progetto Olimpiadi di Matematica - GARA di SECONDO LIVELLO · Italy

In recording the statements of the three defendants at a trial, the clerk was rather careless, and the transcript reads as follows:
Carlo: the culprit is ... ario.
Dario: the culprit is Dario.
Mario: the culprit is ....ario.
Knowing that the culprit lied and at least one of the innocent ones told the truth, what can be concluded?

Pick one

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Official solution

Solution:

The answer is (D). Since the culprit lied, he cannot be Dario, who accused himself. Since one of the innocent ones told the truth, the culprit's name ends in ario, and hence it is Mario. Therefore Mario lied, and hence he accused Dario.

Source: MathNet, licensed CC-BY-4.0. Statement translated into English from it; metadata (topic, difficulty, ordering) added by this project.