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March 13th, 2012, 09:37 PM  #1 
Senior Member Joined: Sep 2008 Posts: 199 Thanks: 0  sample size and confidence interval
To reduce the width of a confidence interval for a mean by onehalf, 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? 
March 14th, 2012, 12:42 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,759 Thanks: 696  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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