A box contains nine bulbs out of which 4 are defective. If four bulbs are chosen at random, find the probability that all the four bulbs are defective.

A. 62/63
B. 125/126
C. 1/63
D. 1/126

Explanation:

Out of nine, five are good and four are defective. Required probability = ⁴C₄/⁹C₄ = 1/126