A box contains nine 40-W bulbs, four 60-W bulbs, and five 75-W bulbs. If bulbs are selected one by one in random order, what is the probability that at least two bulbs must be selected to obtain one that is rated 75 W?

0.7222 or 72.22%

Step-by-step explanation:

The probability that it takes at least two bulbs to pick a 75-W bulb is 100% minus the probability of getting a 75-W bulb with the first pick.

Since there are 5 75-W bulbs out of a total 18 bulbs, the probability is:

There is a 0.7222 or 72.22% probability that at least two bulbs must be selected to obtain one that is rated 75 W

i hope this is what you were looking for.

see attached graph