1. ## Hypergeometric distribution problem

A purchaser receives small lots (N = 25) of a high precision device. She wishes to reject the lot 95% of
the time if it contains as many as seven defectives. Suppose she decides that the presence of one defective in
the sample is sufficient to cause rejection. How large should her sample size be?

2. ## Re: Hypergeometric distribution problem

Originally Posted by pearl
A purchaser receives small lots (N = 25) of a high precision device. She wishes to reject the lot 95% of
the time if it contains as many as seven defectives. Suppose she decides that the presence of one defective in
the sample is sufficient to cause rejection. How large should her sample size be?
Pearl: Please do not post homework problems without showing any effort from your end.

3. ## Re: Hypergeometric distribution problem

Its not given how many defectives are there in the entire lot of 25 items. How do I proceed then?

4. ## Re: Hypergeometric distribution problem

Originally Posted by pearl
A purchaser receives small lots (N = 25) of a high precision device. She wishes to reject the lot 95% of the time if it contains as many as seven defectives. Suppose she decides that the presence of one defective in the sample is sufficient to cause rejection. How large should her sample size be?
I've bolded a relevant part to your previous question. You may not know exactly how many there are but note that the more there are the more likely it is that you would reject. So reducing the number of defectives in the lot will reduce the expected number of defectives in a sample. So ask yourself: Does it make sense to assume there are six defectives? Why or why not? Does it make sense to assume there are eight defectives? Why or why not? Where does that leave you?

5. ## Re: Hypergeometric distribution problem

No. of defectives cant be 6 otherwise the lot will never be rejected.
But it could be anything more than 6. It could be 7 also. Could be 8. How do I decide that.
The purchaser wants a 95% accuracy in her sample. But that deosnt give me any idea on the no. of defectives contained in the lot

6. ## Re: Hypergeometric distribution problem

Does it make sense to assume that all 25 are defective?

7. ## Re: Hypergeometric distribution problem

Originally Posted by Dason
Does it make sense to assume that all 25 are defective?
I m not getting you. If all are defective then the lot will always be rejected.
So if she decided that even 1 defective piece would lead to rejection then at most she needs to have just 1 item in her sample size

8. ## Re: Hypergeometric distribution problem

But will that setup work if there are only 20 defectives? 10 defectives? 7 defectives? The point is that you need to plan for the hardest possible case to detect.

9. ## Re: Hypergeometric distribution problem

alrite..
i think i got it...
thnx

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