http://www.perlmonks.org?node_id=388632


in reply to Spooky math problem

Suppose I have two envelopes. All you know is that they contain different numbers. I randomly hand you one of them. You open it, look at it, then hand it back. You now have sufficient information to, with guaranteed better than even odds, correctly tell me whether I gave you the envelope with the larger number. How?
No, that question actually is:
If I give you a number from a set of two diffrent numbers tell me if you got the small or large number?

My odds of doing that is exactly 50%.

If you sit down and do the algebra, you will find that your probability of being right turns out to be exactly 50% plus 1/2 the probability that you pick a number between my two.
Hmm. If I choose to guess myNumber + epsilon(where epsilon is small enough) I have 50% chance of being between your two numbers and hence have 75% chance of being correct, which is silly:-)

Ok four years late but I got here from this node.