Arminius
(Arminius)
March 31, 2016, 7:44pm
208

phoneutria:

Arminius:

Phoneutria.

[tab]Both A and B have "12"s on their foreheads, and 12 + 12 = 24. So you should know from the premise (12 + 12) that the sum is 24, not 27. The sum must be 24. That is why your solution is false. The sum 27 is not possible because of the premise that both have "12"s on their foreheads.[/tab]
On their foreheads!

[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]

[tab]

Phoneutria, my comment was addressed to you , not to A and B. You have to know that both have “12”'s on their foreheads (so that the sum must be 24 in your calculaltion). That was meant. This premise is given in the riddle.[/tab]
Good luck!