Nobody knows, you cant reply on probability to let you know.
It would be like saying how many times will you get heads if you toss a coin 100 times. The probability is 1 in 2 so you would expect get 50 but you
could get none at all or you could get 100 the 'probability' is the same. Probability has no real effect on the actual result.
So the Drake equation is really a waste of time. You simply have to go out and check to find out.
edit on 28-1-2012 by PhoenixOD because: (no reason given)