If I think of a number between 1 and 1,000, guessing it in 10 yes-no questions is easy... so that's not the puzzle!
Guessing it in 10 yes-no questions, that must be all asked in advance, is also relatively easy... so that's not the puzzle either!
How many questions would you need to guess my number, if you had to ask all questions beforehand, and I also could lie once?
(In reply to Unexpected solution
While it took me a few minutes to get my brain to work the logic, it appears that your question will work, even if the person lies 10 times.
Now show me this solution with one question!
Posted by Leming
on 2005-04-18 00:41:08