Explanation:

The sample space when a dice is rolled, S = (1, 2, 3, 4, 5 and 6)
So, n (S) = 6
E is the event of getting an even number.
So, n (E) = 3
So, the probability of getting an even number P (E) =

Total numbers of favourfable outcomes

Total numbers of outcomje
                               n(E)     =  = 3/6 = 1/2

                           = n(S)