00:01
We have been given some sample data.
00:03
The sample size n is 47, sample mean x -bar is 22 .5 and standard deviation s is 9 .7.
00:12
We want a confidence interval for the population mean.
00:17
So the formula is x -bar, the point estimate, plus and minus the margin of error t s over root n.
00:25
So we're using t here because sigma, the population standard deviation, is unknown.
00:30
If i knew what it was, i'd say we're going to be using z.
00:34
Now some courses, some textbooks, will tell you that when your sample size gets large, then you can just use z anyway.
00:43
This is pretty large.
00:44
We consider it to be n over 30, where some textbooks will say just use z.
00:49
So it's worth checking if your course wants you to do that.
00:52
If so, i will grab the necessary z score for you, and you would just be putting that in instead.
01:00
That would be...
01:00
Okay, i've got it.
01:01
I'll just put in when i put t in.
01:04
So what is t? well, it's based on three things.
01:07
First of all, how many tails the interval will have.
01:12
Well, a confidence interval has two bounds and then tails beyond it, so it is two -tailed.
01:17
What all confidence intervals are? degrees of freedom is n minus 1, so that's 46...