For a given event, what is the result of dividing the number of successful outcomes by the number of possible outcomes?

Dividing the number of successful outcomes by the number of possible outcomes is the definition of the probability of the given event.

P(E)=n(E)/n(S)

example. let the Experiment be throwing a dice. The sample space, all the possible outcomes, is the set S={1, 2, 3, 4, 5, 6 }  and n(S)=6

Let the even E be: getting an even number. The successful outcomes set is  E {2, 4, 6 } and n(E)=3

So probability of getting an even number is P(E)=n(E)/n(S)=3/6=0.5

Probability of the given Event