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JEE Advanced · Mathematics · 32. Probability

Paragraph:

A box \(B_{1}\) contains \(1\) white ball, \(3\) red balls and \(2\) black balls. Another box \(B_{2}\) contains \(2\) white balls, \(3\) red balls and \(4\) black balls. A third box \(B_{3}\) contains \(3\) white balls, \(4\) red balls and \(5\) black balls.


Question:

If \(2\) balls are drawn (without replacement) from a randomly selected box and one of the balls is white and the other ball is red, the probability that these \(2\) balls are drawn from box \(B_{2}\) is

  1. A 1 1 6 1 8 1
  2. B 1 2 6 1 8 1
  3. C 6 5 1 8 1
  4. D 5 5 1 8 1
Verified Solution

Answer & Solution

Correct Answer

(D) 5 5 1 8 1

Step-by-step Solution

Detailed explanation

Let A : one ball is white and other is red
E1 : both balls are from box B1
E2 : both ball are from box B2
E3 : both ball are from box B3
Hence, Prequired=PE2A
= P A E 2 · P E 2 P A E 1 · P E 1 + P A E 2 · P E 2 + P A E 3 · P E 3
= 2 C 1 × 3 C 1 9 C 2 × 1 3 1 C 1 × 3 C 1 6 C 2 × 1 3 + 2 C 1 × 3 C 1 9 C 2 × 1 3 + 3 C 1 × 4 C 1 1 2 C 2 × 1 3
= 1 6 1 5 + 1 6 + 2 1 1
= 5 5 1 8 1
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