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micmom3
03-31-2008, 05:37 PM
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day

Thanks

Subhotosh Khan
03-31-2008, 05:40 PM
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day
What are the z-values of the difference?

micmom3
03-31-2008, 06:49 PM
explain

stapel
03-31-2008, 07:10 PM
explain
Are you saying that you need lessons on z-scores, etc?

Please be specific. Thank you! :D

Eliz.

royhaas
03-31-2008, 07:40 PM
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day

Thanks
There is a simple formula for this kind of sample size problem. It should be in your textbook, possibly in the chapter that talks about confidence intervals for a normal mean with known standard deviation.