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On the island of knights and knaves (where knights always tell the truth and knaves lie), you meet two islanders named Penny and Quinru.

Penny: Both Quinru and I are knaves!

Who is a knight and who is a knave?

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They are

Penny is a knave
Quinru is a knight

Because

if Penny were a knight then it is true Penny is a knave. a Contradiction. so Penny is a knave. Therefore it is false that Penny is a knave AND Quinru is a knave. Therefore Quinru must be a knight

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    $\begingroup$ The real complication here: Why would I trust them to tell me their names? What we actually know is that the one who spoke is a Knave and the other one is either not a Knave or not named Quinru. It could be a mildly interesting puzzle if we knew where that information came from. $\endgroup$ – the-baby-is-you May 11 at 19:34

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