==> probability/killers.and.pacifists.p <==
You enter a town that has K killers and P pacifists.  When a
pacifist meets a pacifist, nothing happens.  When a pacifist meets a
killer, the pacifist is killed.  When two killers meet, both die.
Assume meetings always occur between exactly two persons and the pairs
involved are completely random.  What are your odds of survival?