Answer:
The possibility of gaining the answer, the gate being locked or unlocked is null.
Step-by-step explanation:
The sign behind the guards informs that one guard lies another speaks truth. However if I ask one guard regarding the gate, I wouldn't get the answer as I don't know if the guard is a lier or trustworthy. Therefore, even if the guard is a truth- sayer, I won't believe it. My doubts will remain unanswered.
Hope I gave the correct answer, I did my level best.
Thank you Al