00:01
Okay, in this problem we have to find a 90 % confidence interval for the population mean.
00:06
Now, i don't have any specifics.
00:09
So what we need in order to do that is we need a sample size, right? i'm going to suppose maybe that the sample size is 30.
00:16
And then what we need is a sample mean.
00:19
So i'm going to suppose that my sample mean, and again i'm just making up these numbers, is going to be maybe 45 .3.
00:30
And then we also need a sample standard deviation.
00:33
And i'm going to say maybe that my standard deviation is 3 .1.
00:37
And then the last thing that we need is our z -score that's associated with 90%.
00:43
And that we can just look up online.
00:46
That is going to be 1 .645.
00:49
So our z -score for 90 % is going to equal 1 .645.
00:56
Let me double check making sure.
00:58
All we have to do is look up that on a table or look it up online.
01:02
And yeah, it's 1 .6449, which is 1 .645.
01:06
All right, so with this we can put it into our formula for a confidence interval.
01:10
And that's going to be x -bar plus or minus our z -score for 90 % times our standard deviation over the square root of our sample size.
01:21
All right, so whatever the numbers are that are in your problem, all you need to do is substitute these values in.
01:27
Now z for 90 is going to be 1 .645.
01:30
That's not something you have to make up or something you have to look for...