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?	Choose the correct choice from the following answers
A) 20/66	B) 20/63	C) 20/87	D) 20/98	E) 20/12
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?