00:01
A company wants to know how satisfied their customers are.
00:04
They're going to take a survey but they don't know what sample size is necessary.
00:09
Imagine if they did know the sample size n.
00:11
They'd go ahead, take their sample and find x bar, the sample mean.
00:15
From this they would make a confidence interval to estimate the population mean.
00:21
The formula they would use is x bar, their point estimate, plus and minus the margin of error, z sigma over root n.
00:30
We're just going to focus on the error though, since we've been told that the error should be no more than 0 .6.
00:38
So we'll set this as less than or equal to 0 .6.
00:42
Now if i solve for n, i'll know the sample size necessary to make this true, and that's what we're going to do.
00:48
We have a couple of unknowns here.
00:51
Sigma is the population standard deviation which we've been given, 3 .62.
00:57
Z we get from a level of now as the sample size increases, the sample means become more and more normally distributed.
01:08
That's from the central limit theorem...