## Thinking Mathematically (6th Edition)

$\frac{1}{1000}$
If the odds against event E are a to b, then the probability of the event is given by P(E) =$\frac{b}{a+b}$ The odds against contracting an airborne disease are: 999 to 1 P(E) = $\frac{1}{999 + 1}$ = $\frac{1}{1000}$