00:01
All right, so a number of advertisements seen or heard in a week for 30 randomly selected people are given in the data set.
00:08
And we need to compute the mean and the standard deviation in order to be able to find a 95 % confidence interval.
00:15
And that was done using technology.
00:18
You know, you can do these out by hand, but doing a standard deviation for 30 different data points is a bit of overkill and it will take a long time.
00:26
So if you put all these in a calculator, it'll compute the standard.
00:30
And the mean for you, we get that in the box there.
00:33
We have an sample size of 30.
00:34
Now, for a 95 % confidence interval, we need to find the t score.
00:48
And to do that, we need to find the degrees of freedom, which is n minus 1 or 29.
00:55
And if we go into a t table or use a calculator, and we look at 95 % confidence interval and 29 degrees of freedom, we wind up finding a t score of 2 .05.
01:07
All right.
01:08
So that's the t score we're going to use to construct this interval.
01:11
And the interval itself, the formula, is x bar plus and minus the t score times the standard error, which is going to be the standard deviation over the square root of n.
01:23
And in this case, our x bar is 600 .93 plus and minus 2 .05 is our t score times, 159 .53 is our standard deviation over the square root of 30, which is our n.
01:43
And we're going to compute the stuff to the right of the plus and minus.
01:50
159 .53 divided by the square root of 30.
01:54
And then we're going to multiply that by the t score of 2 .05, which will give us a margin of error of 59 .7...