A box contains nine bulbs out of which 4 are defective. If four bulbs are chosen at random, find the probability that exactly three bulbs are good?  Answers:
A) 20/67  B) 20/63  C) 20/68  D) 20/28  E) 20/27
Required probability   = (⁵C₃ . ⁴C₁)/⁹C₄ = (10 * 4)/126   = 20/63   Answer:20/63
<result>B</result>
A box contains nine bulbs out of which 4 are defective. If four bulbs are chosen at random, find the probability that exactly three bulbs are good?