00:02
To get a confidence interval, we need this formula.
00:05
The sample mean plus or minus the critical value, which i'm calling z star, times sigma, the standard deviation, population standard deviation, divided by the square root of n, our sample size.
00:19
So in this case, the first case, the sample size is, or i'm sorry, the sample mean is 32, that's our x bar.
00:29
We know sigma, the population standard deviation is six.
00:33
And there's 50 items, so square root of 50.
00:38
And then for a 90 % confidence interval, our critical value is 1 .645.
00:48
So now what i'm going to do is find our margin of error for that 1 .645 times 6 over the square root of 50, which is going to be right about 1 .1, we'll call it 1 .396.
01:10
And then to get my interval, i'm going to add and subtract 1 .396 from 32.
01:19
On the low end, it's going to be 30 .604.
01:24
And on the high end, it's going to be 33 .396.
01:40
Now, that's for 90%.
01:42
Now we're going to do the same thing, but for a 95 % confidence interval.
01:48
So the only thing that's going to change here is our critical value...