Odds.
The probability that an event will not occur is calculated by subtracting the probability of the event occurring from 1. Given that the probability of the event occurring is 0.2, the probability that it will not occur is 1 - 0.2 = 0.8. Thus, there is an 80% chance that the event will not occur.
The probability that an event will occur plus the probability that it will not occur equals 1.
If the event in question is A and the probability of A occurring is P(A), then the probability of A not occurring is P(A')=1-P(A).
These events are complementary. Let P(A) = probability event will occur. Then the probability it will not occur is: 1 - P(A).
"Odds".
If the probability of an event occurring is p, then 1-p represents the probability of the same event not occurring. The value of p must lie between 0 and 1.
The complement of an event occurring is that it does not occur.
p/(1-p) the relation between both outcomes.
odds
Probability can not be less than 0 or greater than 1. A probability of 0 means there is no possibility whatsoever of an event occurring. A probability of 1 means that the event is guaranteed to occur no matter what.
Let p = probability the event will occur; and q = probability the event will not occur. The relationship is p=1-q or q=1-p.
If the event is truly impossible, it has a zero probability of occurring. The definition of impossible is "not able to occur, exist, or be done," so that means there's no chance of it happening.