The odds in favor of the occurrence of an event are

We know that,

If odds in favor of the occurrence an event are a:b, then the probability of an event to

 occur is $\frac{a}{a+b}$ which indirectly came from

Probability of the occurrence of an event

$=\frac{\text { Total no.of Desired outcomes }}{\text { Total no.of outcomes }}$

Where, Total no.of desired outcomes = a, and total no.of outcomes = a+b

Given a = 8, b= 13

The probability that the event occurs

$=\frac{8}{8+13}$

$=\frac{8}{21}$

Conclusion: Probability that the event occurs is $\frac{8}{21}$