“The probability of a chain reaction”

It seems to me that either there is some chunk of material that was dropped by mistake, or else that this section makes

no sense. The formula shown, we are told, comes from “easily solving this equation”. But there is no equation,

and the text above that formula does not make much sense either.

Maybe there is some infinite geometric series that is being summed, or maybe there is some

assumption being made that leads to a quadratic equation, to which this is a solution.

However, without the assumption, and without the quadratic equation and justification,

this may be giberrish.

I’d appreciate receiving a reference where the details of this assertion are justified.

Thanks,

Leah Keshet