If I think of a number between 1 and 1,000, guessing it in 10 yesno questions is easy... so that's not the puzzle!
Guessing it in 10 yesno 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?
The first 10 questions would be as Charlie suggests.
Then, I'd number the 10 questions in binary. My question (10+n) would
be: "Did you tell the truth to all questions numbered with a 1 in the
nth position?". Now:

Posted by e.g.
on 20050414 20:55:30 