Standard error of the mean

[miles12]

Hello,

Can any one help, I need the right formula for this problem

A simple random sample of 40 items resulted in a sample mean of 25. The population standard deviation is o=5

(a)what is the standard error of the mean, ox( I cant make the - over the x)

this is my work

40/sqrt5= 8 (is this right)

(b) at 95% confidence, what is the margin of error

If I can just get the formula I may be able to work this out

thanks
J[/i]

 

[daon]

1. You may have that backwards:

\(\displaystyle \L\\ \sigma_m = \sigma/\sqrt{n}\)

Also, in regards to your 2nd question, check out http://davidmlane.com/hyperstat/confide ... rvals.html

 

[miles12]

Thank you

1. You may have that backwards:

\(\displaystyle \L\\ \sigma_m = \sigma/\sqrt{n}\)

Also, in regards to your 2nd question, check out http://davidmlane.com/hyperstat/confide ... rvals.html