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Well, I've got this problem which just is confusing me greatly.

"A sample of 4 different calculators is randomly selected from a group containing 15 that are defective and 33 that have no defects. What is the probability that at leastone of the calculators is defective?"

Now, we're in the binomial probability problems section so I think of the criteria and see that it fails that the events are mutually exclusive so it cannot be that.

I don't have the answer and really just need the method for how to solve it. Crunching numbers is the easy part.

I think P(>=1) = P(X=1 or X=2 or X=3 or X=4)

= P(X=1) + P(X=2) + P(X=3) + P(X=4) - P(1 and 2 and 3 and 4) which would be the addition rule, but I have no idea.

For those probabilities I would do 1/48, 1/47, 1/46, 1/45 and ... no idea for the last one. All that we've done is addition rule with two probabilities.

Im very lost.

Any ideas?

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# Argh. Probability question

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