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?

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 n-th position?". Now:

Posted by e.g. on 2005-04-14 20:55:30