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 What does "in advance" mean?
by Erik O.)
You must write all the questions first, and only then you'll get all
the answers -- you cannot have any question depending on previous