00:01
All right, so we have a thing for the minimum size required to find a 92 % confidence interval for the mean cost for this thing.
00:13
It doesn't matter what it is, but it's going to with this thing.
00:16
Within 100, well, it's starting a cost, so it's dollar.
00:18
So within $145.
00:22
In the previous studies have shown the standard of deviation is this amount.
00:26
So let's get the z score first.
00:28
Actually, let's do the formula.
00:29
I like what we need.
00:32
So the margin of error formula is equal to z alpha over 2 times sigma over root n.
00:49
So this is our formula.
00:50
And we want to get n.
00:52
And we know some of this stuff already.
00:55
But let's do it.
00:56
Let's do a little algebra, get n by itself.
00:57
So let's see, we're going to multiply by root n and simultaneously divide by l show it.
01:06
We get a margin of error, equal z alpha over two, sigma.
01:13
Now we're gonna divide by margin of error.
01:23
There we go.
01:24
Oh, one last step, square both sides.
01:34
And there we go.
01:35
There's our n, z alpha over two, sigma over n, and all this stuff is squared.
01:44
So now it's a matter of substituting in what we have.
01:47
So the first thing we need to figure out the z score...