00:01
We have been given some sample data.
00:02
Sample size n is 4.
00:05
Sample mean x bar is 60.
00:07
Sample standard deviation s is 14.
00:10
We want a confidence interval for the population mean.
00:14
The formula for this is x bar, point estimate, plus and minus the margin of error, t s over root n.
00:21
T is our critical value here.
00:23
It's not the only critical value, there's also z, and z is preferable but we cannot use it because sigma, population standard deviation, is unknown.
00:33
So we have to use t instead.
00:35
To get t you need three pieces of information.
00:38
First that you want the two -tailed value.
00:40
Our interval is going to have two bounds and tables beyond those.
00:45
Alpha is one minus confidence.
00:48
We want 90 % confidence making this 10 % and degrees of freedom is n minus one, so that's three.
00:57
Put that into your t value table or software of your choice to get the critical value 2 .353.
01:05
Okay now let's put these values into our formula...