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.	Select the correct option
A) 20/61	B) 20/63	C) 20/62	D) 20/87	E) 20/18
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.