The odds of an event is the ratio of the probability of an event to the probability of its complement.
To find the odds of an event with probability of 1/2:
1. Find the probability of the complement:
The probability of the complement (-E) is equal to 1 less the probability of the even (E):
2. Find the odds:
Or:
Then, ther oddds of an event ocurring, given the provavility 1/2 are 1:1 (1 to 1)