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?  Pick.
A) 20/68
B) 20/63
C) 20/62
D) 20/61
E) 20/67
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?