The rule of addition applies to the following situation. We have two events from the same sample space, and we want to know the probability that either event occurs.
Rule of Addition If events A and B come from the same sample space, the probability that event A and/or event B occur is equal to the probability that event A occurs plus the probability that event B occurs minus the probability that both events A and B occur.
P(A ∪ B) = P(A) + P(B) – P(A ∩ B)
Note: Invoking the fact that P( A ∩ B ) = P( A )P( B | A ), the Addition Rule can also be expressed as
P(A ∪”; B) = P(A) + P(B) – P(A)P( B | A )
So it’s like the possibility that the space shuttle will burst into flames (A) or fall apart (B) while crashing into the moon? I think this raises the question of why both can’t happen but maybe that’s a different topic. I guess it depends on if it’s a scheduled malfunction (referencing Destination: Void by Frank Herbert) .
Kryptos - Beyond K4 
What are the odds health care reform will fail while the economy does?
It’s all public opinion.
If we think things’ll get better then we’ll spend more and the economy will get better.
Everyone and their monkey’s uncle has suggested health care reform over the past 30+ years regardless of party. The health care system is the biggest resistance to reform and we’re gullible enough to listen to them every time.
I liked Destination Void but it always made me feel stupid every time I read it.
Just like Kryptos