I was thinking about this today so I decided to ask it here. I know the rule of adding probabilities. As I was taught in grade school "OR" typically means add and "AND" typically means multiply.
Suppose there is a jar with a red, blue, green, and yellow ball. The probability of picking a red ball is 25%. The probability of picking a red ball, putting it back, AND then picking a green ball is 12.5% (25% * 25%). The probability of picking either a red OR a green ball on the first try is 50% (25% + 25%).
These are independent events. Now lets take another set of independent events.
The weather man said there is an 80% chance of rain. This means it should rain 80% of the time I assume. If you looked back at the past 100 days with an 80% rain chance it should rain on ~80 of them.
A girl hooked up with 5 of our 10 mutual friends. I have a 50% chance of hooking up with her too.
Rolling an even number on a dice carries a 50% probability.
If it rains OR I hook up with the girl OR I roll an even number on the dice then I win. If any one of these things happen I win, just like if I pick a red or a green ball, it doesn't matter if its red or green. With that being said the probability that it rains or I hook up or I roll an even number is 180%. This is not true because it is remotely possible that none of those things happen.