Posted by **David** on Tuesday, February 24, 2009 at 2:56pm.

Two independent events, A and B, satisfy Pr(A) = 0.6 and Pr(B) = 0.3. In the case of Pr(A or B), why isn't the answer 0.3? We are looking at the probability of A or B. I choose B.

Thank you!

- Probability/Statistics -
**drwls**, Tuesday, February 24, 2009 at 4:02pm
The answer is Prob(A) + Prob(B) - Prob (A + B)= 0.6 + 0.3 - 0.18 = 0.72

The last term avoids double counting of the occurence of both A and B, which satisfied the "A or B" criterion only once.

The answer is certainly not 0.3, since 60% of the events are A and satisfy the A or B requirement

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