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Andrew and Bob are talking to each other, but we don't yet know who is who.

The guy in the blue shirt says, "I am Andrew."

The guy in the red shirt says, "I am Bob."

If at least one of them lied, what color shirt is Andrew wearing?

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The guy in the blue shirt says, "I am Andrew."

If he is a liar, he is BOB.

The guy in the red shirt says, "I am Bob."

If he is not a liar, he is BOB and hence ANDREW must be speaking the truth.

This is

a contradiction as at least one of them lies.

Hence,

both of them lies i.e Andrew is the one in RED shirt and BOB in BLUE.

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Suppose only the guy in blue lied, then he was in fact Bob. But then the guy in red would be lying also, as the guy in red said that he was Bob, who should be Andrew in fact. This led to a contradiction.

Suppose only the guy in red lied, then he was in fact Andrew. But then the guy in blue would be lying also, as the guy in blue said that he was Andrew, who should be Bob in fact. This led to a contradiction.

Since there was at least one person lying, therefore the guy in blue was Bob and the guy in red was Andrew. Both of them lied.

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Since they both claim to be a different one of the available options, they're either both "truthing" or both lying.

Since at least one of them is lying, they're not both speaking the truth and so they have to be both lying and so the one claiming to be Bob is actually Andrew and is wearing a red shirt.

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Suppose Andrew is telling the truth, Bob could still be lying. He could be called Colin, for example. Or he could even be called Andrew too.

So I would say there is not enough information.

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  • 6
    $\begingroup$ "Andrew and Bob are talking to each other, but we don't yet know who is who." $\endgroup$ – greenturtle3141 Jan 22 '17 at 20:00

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