Wait... aren't you missing a 1- at the beginning? If there are two stars, and the probability is 0.9 for each one, the probability of life anywhere is not 0.01, but 0.99. You've given the probability of life being nowhere

Actually if you work this out fully mathematically. You get a very simple equation.

Start with the known principle that there is an infinite amount of space out there. Next that in this infinite amount of space there exists some number of stars (the exact amount isn't needed, for our sake it is also an infinte number). This means there should be an infinite number of planets in an infinte number of stars. However since not every planet contains life on it, there must be a finite number of planets containing life.

This leads to a simple equations of the probability of life on any planet : (Number of planets that could possible containing life)/(number of planets)

Gives you a finite number divided by an infinite number. Making the probablity of life on ANY planet to = ZERO.

(YUP folks technically we should not even exist)