Let's pose this question a different way: what are the chances that one out of all possible events is going to happen? What are the chances that, if I roll a die, I will roll a 1, 2, 3, 4, 5, or a 6? What is the probability, if I flip a coin, that the outcome will either be heads or tails? When we take every possible outcome and add their probabilities together, the sum of the probabilities will be 100%, or 1.
Example: Coin Toss: Prob of Heads (.5) plus Prob of Tails (.5) = 1 Dice roll: 1/6 (odds of rolling any given number) times 6 (number of possibilities) = 1
