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12 people are asked questions in succession in a random order and exactly 3 out of 12 people know the answer. The probability that the 6 t h person asked is the 2 n d person to know the answer, is

Options

  1. A10 21
  2. B3 22
  3. C7 11
  4. D5 12

Correct answer

B. 3 22

Step-by-step solution

6 t h Person asked is the 2 n d person to know the answer ⇒ In the first five people there must be exactly one person who knows the answer Required probability = 9 C 4 × 3 C 1 12 C 5 × 2 7 = 9 × 8 × 7 × 6 × 120 × 3 24 × 12 × 11 × 10 × 9 × 8 × 2 7 = 3 22

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