00:01
We are looking at a normal distribution.
00:03
I'm going to start by drawing it.
00:09
Mean, mu, is 235.
00:15
The standard deviation, sigma, is 20.
00:18
We've been given a value.
00:20
We don't know what the value is, we're going to work out.
00:22
But we do know it's higher than 15 % for this distribution.
00:27
So this cholesterol level is down here somewhere.
00:30
So this area is 15%, or 0 .15.
00:34
And the area to the right is just, 0 .85.
00:37
So we call this the 15th percentile, the value where 15 percent are lower.
00:44
And we want to find it.
00:46
Okay, we can do that because we have the probabilities, we can turn those probabilities into a z score and then from a z score into a cholesterol level...