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.
A. 20/31  Choose the correct answer:
A) 80/63	B) 20/63	C) 20/93	D) 20/03	E) 20/53
Explanation:   Required probability = (⁵C₃ . ⁴C₁)/⁹C₄ = (10 * 4)/126 = 20/63   Answer: Option 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.
A. 20/31