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March 13th, 2012, 09:37 PM   #1
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sample size and confidence interval

To reduce the width of a confidence interval for a mean by one-half, when the original sample was of size 36, how many additional sample items are needed?

Is there sufficient information to answer this question? If so, how do i solve it?
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March 14th, 2012, 12:42 PM   #2
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Re: sample size and confidence interval

The confidence interval ~ 1/?n. You need to multiply the sample size by 4 to cut the interval in half. So add 108 more samples.
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