Sharon, as John has already said you always can argue that any problem statement is incomplete if you want. What if the guard you asked was deaf (and not his brother). What if he didn't understand English (that was not stated explicitely!), what if he did understand and did understand English but your question was to difficult for him to find out how to respond with a lie. And so on. You just have to stop stating conditions at one point and hope for the problem solvers to think a bit.

What is the response to A + B + C = ? with A = 2, B = 4 and C = 5? You think it is 11? I say You're wrong. Nowhere did I state explicitely that I was talking about base 10 addition. And by the way who did tell you that the + sign signifies what you consider addition. I forgot to state that too. There is no end to this game if someone is willing to question everything.

Wolfgang