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) 20/65	B) 20/63	C) 20/45	D) 20/29	E) 20/20
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?