Answer
$\frac{1}{29}$
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 deep-vein thrombosis are 28 to 1.
P(E) = $\frac{1}{28+ 1}$ = $\frac{1}{29}$