- #1
fateswarm
- 18
- 0
If we have two disjoint events then it comes to reason that P(A or B) = P(A) + P(B) - 0
However, if I rewrite it as 1 - P(A' and B') how is the numerical result going to be the same? (without re-writing it back as 1 - P ((A or B)')).
I assume it is 1 - P(A'|B')P(B')
But how is P(A'|B') calculated in there?
For example:
Let's assume P(A) = 0.12 and P(B) = 0.17, and we know that P(A and B) = 0 by being disjoint.
Hence P(A or B) = 0.12 + 0.17 -0 = 0.29
Now, P(A or B) = 1 - P((A or B)') =
= 1 - P(A' and B')
If I do
= 1 - P(A')P(B') = error, the result is 0.2696. It's as if the events were not disjoint obviously.
if I do
= 1 - P(A'|B')P(B')
And I know that P(B') = 1 - P(B) = 0.83
then it comes to reason that for the result to be correct
P(A'|B') must be 0.8554
Now how is that found on its own?
I currently assume that I'm not supposed to find it directly at all but go with other methods around it.
However, if I rewrite it as 1 - P(A' and B') how is the numerical result going to be the same? (without re-writing it back as 1 - P ((A or B)')).
I assume it is 1 - P(A'|B')P(B')
But how is P(A'|B') calculated in there?
For example:
Let's assume P(A) = 0.12 and P(B) = 0.17, and we know that P(A and B) = 0 by being disjoint.
Hence P(A or B) = 0.12 + 0.17 -0 = 0.29
Now, P(A or B) = 1 - P((A or B)') =
= 1 - P(A' and B')
If I do
= 1 - P(A')P(B') = error, the result is 0.2696. It's as if the events were not disjoint obviously.
if I do
= 1 - P(A'|B')P(B')
And I know that P(B') = 1 - P(B) = 0.83
then it comes to reason that for the result to be correct
P(A'|B') must be 0.8554
Now how is that found on its own?
I currently assume that I'm not supposed to find it directly at all but go with other methods around it.