“Suppose you are on a game show, and you are given the choice 
of three doors: Behind one door is a Rolls Royce car and behind 
the others, goats. Let's assume that you would prefer a Rolls Royce 
to a goat. You pick a door, say No.1, and the host, who knows 
what's behind the doors, opens another door, say No.3, which has 
a goat. He then says to you, "Do you want to pick door No. 2? 
Is it to your advantage to switch your choice?”