CA Foundation · Quantitative Aptitude · Probability
For two events A and B, P(A) = 0.6, P(B) = 0.5 and P(A ∩ B) = 0.3. What is P(B | A)?
P(B | A) equals P(A ∩ B) divided by P(A), which is 0.3 divided by 0.6, giving 0.5. The conditional probability uses the given event A as the base, so dividing by P(B) would wrongly give P(A | B) instead.
- A0.5Correct
- B0.6
- C0.3
- D0.18
Explanation
P(B | A) = P(A ∩ B) / P(A) = 0.3 / 0.6 = 0.5. Option 0.6 would result from dividing by P(B) instead, which gives P(A | B). Dividing by the wrong base is the key error.
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