We know that, between 1 to 100 half numbers are even and half numbers are odd i.e., 50 numbers (2, 4, 6, 8, …, 96, 98, 100) are even and 50 numbers (1, 3, 5, 7, …, 97, 99) are odd. So, both events are equally likely.
So, probability of getting even number = 50/100 = 1/2
and probability of getting odd number = 50/100 = 1/2
Hence, the probability of each is 1/2