A box contains 9 bulbs, of which 4 are faulty. If 4 bulbs are selected randomly, what is the probability that there is at least one working bulb among them?

Explanation

To find the probability of having at least one good bulb, it's easier to calculate the complement — the probability that all selected bulbs are defective. The total number of ways to choose 4 bulbs from 9 is C(9,4) = 126. The number of ways to choose 4 defective bulbs from the 4 defective ones is C(4,4) = 1. Therefore, the probability that all selected bulbs are defective is 1/126. Hence, the probability of having at least one good bulb is 1 - 1/126 = 125/126.