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Given this joint probability distribution table

     |   A   |   B   |   C  
X    | 0.15  | 0.03  | 0.07
notX | 0.05  | 0.25  | 0.45

I've to calc the following probabilities

P(B or X) = ?
P(C or notX) = ?

So far I got this solution:

P(B or X) = 0.15 + 0.03 + 0.07 + 0.25 
P(C or notX) = 0.07 + 0.45 + 0.05 + 0.25

but I'm very unsure...

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1  
This looks fine to me, though this isn't so much a question as it is procedural confirmation. – Jonathan Thiele Jun 13 '12 at 17:31
ok, sorry for that! – user1308532 Jun 13 '12 at 17:41
2  
I agree with Jonathan. What you did to compute P(B or X) was to take P(X and A)+P(X and B) + P(X and C) to get P(X). Then you need to count all the probabilities associated with B occurring but not X ( you do this to avoid double counting). That is the term with the value 0.25. You use the same idea for the second probability. – Michael Chernick Jun 13 '12 at 18:00

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