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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?

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pedrocarratore

Answer:

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:

[tex]P(X\geq 2) = 1 - P(X=1)\\P(X\geq 2) = 1 -\frac{5}{18}\\ P(X\geq 2)=0.7222[/tex]

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

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