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) 20/69
B) 20/63
C) 20/61
D) 20/66
E) 20/63
Explanation:   Required probability =   = (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.