The point estimate of the mean conversation length is the sample mean,Originally Posted bybombo31

so in this case it is 8.5 minutes. The margin of error of this estimate is

usually the standard error (SE) of the mean which is the population standard

deviation (SD) divided by the square root of the sample size. But we usually

use the sample SD as we don't know the population SD.

Now the problem you are given a variance (which is the square of the SD)

but with units of minutes - its units should be minutes squared. But let's

assume that this is a typo and the variance is 9 minutes squared, so the

SD is 3 minutes. Then the SE of the mean is 3/sqrt(45)~=0.447 minutes.

So your point estimate of the mean conversation length is 8.5 minutes with

a standard error of ~=0.477 minutes.

RonL