Ask him how many fingers you are holding upsocialtangent said:This one isn't too impossible, but it's something my math teacher told me that amused me.
There are two towns, Town A and Town B. People from Town A will always tell the truth, and people from Town B will always tell a lie. You are exactly in the middle between the two towns, and there is somebody there. What do you ask him to find out what town he's from?
The person will be forced to either tell the obvious truth or an obvious lie