You are to meet Bob and his brother again. Imagine you still don't know which one of them is Bob, and wether or not Bob always lies or tells the truth. In other words, let's say you never solved the first problem.

But this time, your task is to find out wether or not Bob, whichever brother he is, will lie to you.

It is possible to find this out with a short question to either one of the brothers. (A question consisting of four to five words.) What will you ask?

(pointing at the other guy to the one being asked)
"would he say bob lies?"

4 cases are possible

a. bob is truthful:
i. you ask bob, he says "Yes" (truthful)
ii. you ask brother, he says "Yes" (lying)

b. bob is a liar:
i. you ask bob, he says "No" (lying)
ii. you ask brother, he says "No" (truthful)

so, you get a straight answer, with 5 words, plus a bit of body language, but there was nothing in the question saying that wasn't allowed.

Posted by ubergeek on 2002-12-25 23:24:04