Final answer:
The probability of an event not happening is 9/10, and by definition of odds comparing favorable to unfavorable outcomes, the odds of the event not happening are 9:1.
Step-by-step explanation:
If the probability of an event not happening is 9/10, to find the odds of the event not happening, we need to understand the relationship between probability and odds.
Probability is the ratio of the number of favorable outcomes to the total number of possible outcomes, while odds compare the number of favorable outcomes to the number of unfavorable outcomes.
In this case, the probability of the event not happening is 9/10, which means for every 10 attempts, the event does not happen 9 times and happens once.
Therefore, the odds of the event not happening are 9:1. That is, for every one time the event happens, it does not happen 9 times.