Events A and B satisfy P(B) = 1/2 and P(A and B) = 2/5. Find P(A | B).

Answer and explanation

Correct answer: D. 4/5

  1. Step 1: Use P(A | B) = P(A and B) / P(B).
  2. Step 2: P(A | B) = 2/5 / 1/2 = 4/5.
Answer
4/5.
Why not the others: '1/2' divides by P(A) instead of P(B), giving P(B | A); '1/5' multiplies the two probabilities; '2/5' gives the joint probability, not the conditional one.

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