# Chapter 11 - Counting Methods and Probability Theory - 11.6 Events Involving Not and Or; Odds - Exercise Set 11.6: 91

$\frac{1}{1000}$

#### Work Step by Step

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) = $\frac{1}{999 + 1}$ = $\frac{1}{1000}$

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