[tab]I know that, but they don’t. All they know is the other dude has a 12 and that the total is either 24 or 27.

A 1a: If B had a 9, I’d have a 15.

1b: B has a 12, therefore I don’t have a 9.

1c: 12+12=24 and 12+15=27, therefore the number on my forehead is either 12 or 15

A answers no

B 1a: If A had a 9, I’d have a 15.

1b: A has a 12, therefore I don’t have a 9.

1c: 12+12=24 and 12+15=27, therefore the number on my forehead is either 12 or 15

1d: A answered no on the first round, so he doesn’t know whether the number on his forehead is 12 or 15 either.

1e: If the number he sees on my forehead was 15, he would know for sure that his is 12, since 15+15 is not a valid option.

1f: Since he does not know for sure he must see a 12 on my forehead.

B answers that his number is 12

I change my answer to ONE"[/tab]

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