Tuesday, September 30, 2008

A Classic from Logic

If you ever studied logic, you have definitely seen this question. I found it in Enderton though I'm not sure that it is originally from there.

You are in a land inhabited by people who either always tell the truth or always tell falsehoods. You come to a fork in the road and you need to know which fork leads to the capital. There is a local resident there, but he has time only to reply to one yes-or-no question. What question should you ask so as to learn which fork to take?

An easier question is: if you just wanted to figure out whether the resident was a liar or not, what would you ask?

1 comment:

Anonymous said...

you would ask,"is this the direction the other person will tell me to take" For example, if the correct direction was to the right and you pointed to the left, and if the person you saw was a liar, then he'd say yes (meaning he'd lie because the truthful people would say the right) If he was a truthful person, then he would still say yes, because they would know the liars would say the opposite of the truth. From any of those answers, you'd just do the opposite of what they say and go to the right.