There is a question in my text that list an answer in the back of the book that seems wrong to me.(adsbygoogle = window.adsbygoogle || []).push({});

It is,

"Four microprocessors are randomly selected from a lot of 100 microprocessors among which 10 are defective. Find the probability of obtaining no defective microprocessors."

There are C(100,4) ways of selecting 4 microprocessors from 100 and this is our sample space. There are 90 non-defective microprocessors and so there are C(90,4) ways to select a non-defective microprocessor. So our number of out comes of the event is C(90,4) and so the probability of the event is

P(E)=C(90,4)/C(100,4).

The answer in the back of the text book is given as

C(90,10)/C(100,10)

This answer does not make much sense to me since we are selecting 4 things and not 10 things. Am I right or is the book right?

Thanks

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# Homework Help: Discrete probability

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