1/2 of 1 in 1,000,000
Two passengers are boarding a plane and discussing about plane safety.
A : I don’t think that we are safe to board the plane. Maybe there will be a guy carrying a gun and will do something dangerous.
B : Don’t be ridiculous. The statistics show that the possibility of a man carrying a gun in a plane is one in a million. Besides, I reduce the possibility to half.
A : How can you be so sure?
B : Well, because I carry the gun myself and I am not going to shoot at myself or you.