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?

The question is"Is Bob a lair".

If you ask bob and he is a liar, he will say no.

If you ask bob and he is not a liar, he will say no

If you ask his brother and he is a liar he will say yes

If you ask his brother and he is not a liar he will also say yes

So if the person you ask say no, its bob and if he say yes its his brother

                           

Posted by Sean on 2005-10-27 11:01:58