help w/ what size sample to be 95% confident (sick days)

[micmom3]

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

 

[Deleted member 4993]

Re: Please help

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]

Re: Please help

explain

 

[stapel]

explain

Are you saying that you need lessons on z-scores, etc?

Please be specific. Thank you!

Eliz.

 

[royhaas]

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.