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 one:
A) 20/69
B) 20/63
C) 20/62
D) 20/29
E) 20/61
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?