00:01
Okay, so here we're going to make a 95 % confidence interval.
00:03
We're assuming that our population is normally distributed, which is nice.
00:07
We have a sample of size 30, our mean from our sample is 80, and our standard deviation from our sample was 11 .2.
00:18
First, we have to find the critical value, which is t star.
00:22
Our degrees of freedom, remember degrees of freedom is equal to n -1, so our degrees of freedom here is 29.
00:28
That's going to be important because you can't find a t -star without knowing your decrease of freedom.
00:34
I go to my t -table, and i go to the degrees of freedom 29, and i go over to the column that says, sorry, degrees of freedom 29, and go to the column that says 95 % confidence, okay, and go all the way to the bottom where it goes, it'll either say, like, critical value or infinity degrees of freedom, depending on what you're kind of looking at there.
01:08
Okay, or sorry, not infinity degrees of freedom.
01:12
We're just looking at 29 degrees of freedom.
01:15
So i go to 29 degrees of freedom, 95 % confidence, and i get 2 .045, so my critical value for t starts.
01:27
Okay.
01:27
Next i'm going to calculate my margin of error.
01:34
So remember that the confidence interval has this.
01:37
It's going to be my x bar plus or minus my margin of error.
01:42
And the way to calculate a margin of error for this type of a confidence interval is t star times s over the square root of n.
01:54
So i'm assuming that the e there is that they want that margin of of error...