Twelve men are in a room, some of them always tell lies, while the others always tell the truth.
The first man says: "None of us is a truth teller."
The second man says: "At most one of us is a truth teller."
The third man says: "At most two of us are truth tellers."
The twelfth and last man says: "At most eleven of us are truth tellers."
How many of them are liars ?
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When using the phrase "at most", the bigger the number, the truer it becomes. So, if the twelfth man is a Knight, then the first man's statement would be inevitably became a lie. Therefore, with any additional Knight, another knave would have to appear to counter the balance.
Answer = 12/2 = 6 knaves.