A total of nine bulbs are in a box, with four of them being faulty. If you randomly select four bulbs, what is the probability that every bulb chosen is defective?

Explanation

Among the nine bulbs, there are four defective and five functional ones. The probability that all four selected bulbs are defective is calculated by the ratio of combinations of choosing 4 defective bulbs out of 4 to the combinations of choosing any 4 bulbs out of 9, which is 4C4 / 9C4 = 1 / 126.