# sample size, sampling error

• April 21st 2009, 04:16 AM
lalalamaths
sample size, sampling error
could someone please explain the concept of sampling error? i can't really find it in my text book
ahh thanks :)
also i am stuck on two more problems. (last ones, i swear! haha)

st dev=1200
want a 95% confidence interval for the population value of annual telephone expenditure with an error of estimation (sampling error) no greater than $50 what sample size should be used? suppose that we want a 95% confidence interval for the population value of annual telephone expenditure that is no wider than$100
what sample size should be used?
• April 24th 2009, 03:48 AM
mr fantastic
Quote:

Originally Posted by lalalamaths
[snip]
st dev=1200
want a 95% confidence interval for the population value of annual telephone expenditure with an error of estimation (sampling error) no greater than \$50
what sample size should be used?

[snip]

Assuming a normal distribution, solve $z_{\alpha/2} \cdot \frac{\sigma}{n} = 50$ for $n$ where the other symbols have the usual meaning and you've been given their values.