Est. 1998 — 27 years of woodworking knowledge
Friday Puzzler -- Three Brothers
Alex Y
Alan, Bob, and Carl are three brothers who look so much alike that I can't tell them apart. I meet one of them on the street, and need to know if it is Bob, to whom I need to repay a loan. (I don't owe any money to the other two.)
I know that Alan always tells the truth, while Bob and Carl always lie. What one question can I ask the brother I meet on the street to determine if I owe him money?
Re: Friday Puzzler -- Three Brothers
JohnV
How much do I owe you?
Sorry, but no
Alex Y
You owe Bob $10.
The person you meet answers "$20". Could be either Bob or Carl lying.
Re: Sorry, but no
JohnV
But only if the actual debt is $20
Re: Sorry, but no
JohnV
This presumes that those two don't know the amount.
Re: Sorry, but no
Alex Y
I'm saying the actual debt was $10. If you ask the person on the street, and he says$20, who is it, and how do you know?
Re: Friday Puzzler -- Three Brothers
Ed Wozniak
Are you Carl? If the answer is yes you are talking to Bob.
Correct!
Alex Y
The whole loan bit was a decoy--it was really just the question of finding out if you were talking to Bob.