Given the odds of an event is 3:8, you can state that the event will occur in 3x cases (favorable outcomes) and the event will not occur in 8x cases. In total there are 11x ways of all possible outcomes for the event.
Use theoretical definition of probability:
[tex]Pr=\dfrac{\text{the number of favorable outcomes}}{\text{the number of all possible outcomes}}.[/tex]
Then the probability is
[tex]Pr=\dfrac{3x}{11x}=\dfrac{3}{11}.[/tex]
Answer: [tex]\dfrac{3}{11}.[/tex]
