00:01
We have been given some sample data.
00:03
Sample size n is 30, sample mean x -bar is 92, sample standard deviation s is 9 .6.
00:13
We want the margin of error for a 99 % confidence interval for the population mean.
00:20
The formula for such a confidence interval would be x -bar, the point estimate, plus and minus the margin of error, t s over root n.
00:31
S over root n is our estimate of the standard error, sigma over root n.
00:36
T is for critical value.
00:38
It's not the only critical value, there's also z, but we do not meet the requirement to use z because sigma, the population standard deviation, is unknown.
00:49
So we have to use t.
00:51
To find t you need three pieces of information...