00:01
We are looking at making a confidence interval for the number of books people read in a year.
00:05
So we want the population mean.
00:07
The formula for a population mean is x -bar, the sample mean, the point estimate, plus and minus the margin of error.
00:17
I'm going to be using zs over root n.
00:20
We have s here because we do not know the population standard deviation.
00:25
Z is our critical value.
00:27
Now z isn't the only critical value you might use.
00:30
You might use t.
00:31
So why am i using z? well z is better, but there are requirements.
00:36
To use z, either sigma, the population standard deviation, must be known, which we don't need, or n is large.
00:45
You have a large sample.
00:47
And really, anything over 30, you could start using z.
00:51
So 1015, definitely a large sample.
00:56
So if we go through the information, n, sample size, is 1015.
01:02
X -bar, the sample mean, is 11 .3.
01:07
S, the sample standard deviation, is 16 .6...