You need to use something call binomial probability. Which states that if the probability of an event is . Then the probability of that even happening out of times is,Originally Posted byKiwigirl

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Over here, and , the only thing changing is .

Now we calculate the exact probability of each event.

Here is a table,

Just as, a check we can see that they add up to one. Actually 1.001 because I approximated. Next the probabilty of exactly 0 is not impossible it is almost impossible hence the significant digits. Now, you can answer your questions. For example, the most likely is when thus, by probability theory you should chose 7 good ones and 1 bad iris bulb. You should we able to answer everything else from here. For example, at most 5 means you need to add up all from and to get your answer.