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# STATISTICS, finding the sample size watch

1. I have a really hard time solving this kind of problems. I would really appreciate some help before my exam .

A firm is thinking of selling one more product if the proportion of customers who wants to buy it is at least 20%. To examine if this is the case the firm takes a sample of 100 customers and they will reject the null hypothesis (H0) if the population proportion who says they are going to buy the product is at least 27%.
(Some questions are followed but I already know them)

Now the circumstances are changed.
The person thinks that the probability to NOT reject the null hypothesis should be at least 99% if the population proportion is 17%. He also thinks that the probability to reject the null hypothesis should be at least 99% if the population proportion is 27%
QUESTION: What sample size is required under these circumstances?

A really have problems with finding out the sample size when its all about population proportions and using the power and error 1 and 2… Can anyone explain how to solve this problem and also maybe help me to understand how I should think when I get these problems?

Many thanks,
2. If it helps the answer is n>= 365
3. Anyone know?

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Updated: August 9, 2009
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