00:01
Okay, let's find the 95 % confidence interval for a couple of situations.
00:05
Our first situation is we have a sample size of 50.
00:10
We have a sample mean of 27 .7.
00:13
We have a standard deviation of 6 .12.
00:17
Okay, so first, because we don't have a population standard deviation, actually we don't have any population information at all.
00:25
We have to do a t -test here.
00:27
Sorry, a t -interval, right? so we can't do a z -interval.
00:33
And to find this, we go to the stat button on our ti -83 or 84 calculator.
00:41
You scroll over to tests and then you scroll down until you get to the option t -interval, which is usually option number 8, but it might change depending on your...
00:58
All right, once you get that, you want to make sure that your input is selected on stats, not data, because we don't have the actual data.
01:08
We just have the given stats.
01:11
And then we fill in all of our information here, our sample mean, our sample standard deviation, and then our sample size of 50.
01:23
And then your c -level is going to be what your confidence percentage is.
01:28
So here we want a 95%, so our c -level will be 0 .95, right? once we go to calculate, all this information is going to give us a confidence interval of 25 .961 to 29 .439.
01:56
That's going to be your confidence interval if you're given the actual stats.
02:04
Now let's say that we're given 20 different data points, but this time we are given the population mean and the population standard deviation, right? so now for like this, now for this, we'd use a z -interval because now we have population information.
02:39
So now we still go to stat tests, but now instead of like a selecting eight, we select option seven, z -interval on the stat menu...