CA Foundation · Quantitative Aptitude · Probability
For two events A and B, P(A) = 0.6, P(B) = 0.5 and P(A ∪ B) = 0.8. What is P(A | B)?
P(A | B) equals 0.6. First find P(A and B) = 0.6 + 0.5 − 0.8 = 0.3 using the addition rule, then divide by P(B) = 0.5, giving 0.3/0.5 = 0.6.
- A0.2
- B0.3
- C0.4
- D0.6Correct
Explanation
P(A∩B) = P(A) + P(B) − P(A∪B) = 0.6 + 0.5 − 0.8 = 0.3. So P(A|B) = 0.3/0.5 = 0.6. The value 0.3 is just the intersection, which is the mistake of not dividing by P(B).
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