Consider the following game (somewhat similar to Bulls and Cows): player A selects a permutation of $n$ different numbers, say $1$ to $n$. Player B then has to guess the permutation: he suggests some permutation and A has to reveal which numbers are exactly at their right place (but nothing else). Player B then guesses again, and so forth, until he gets the right permutation.
Question: supposing B's best strategy, what is the worst-case number of guesses (including the last right guess) he would have to make?
Note: it is easy to see that the upper bound on the worst case is $n$. The direct analysis for $n=3$ and $4$ seems to suggest that it is exactly $n$, but I can't quite prove the lower bound.
You can probably argue something like the following: $A$ can choose the permutation while answering the questions of $B$ in such a way that it is consistent with the answers given so far and makes it as hard as possible for $B$ to get it right soon. Then, when $B$ asks the first question, $A$ just chooses a permutation where no digit is in the right spot. Then $B$ asks another permutation and $A$ chooses a permutation for which no digit is in the right place in the first nor second of $B$'s guesses. This can go on $n-1$ times (you should be able to prove this, I hope, since I have not done it myself). In the $n$'th turn, $A$ can not avoid losing.