00:01
Hey there, welcome to numerate.
00:03
We have red blood count, right? so for a population of adults, it's distributed normally with a mean of 5 .4 million cells and a standard deviation of 0 .4 million.
00:16
We're going to find a, so what is the minimum red blood count for the top 25%.
00:22
So the top 25 % basically means, whenever you see top, it's actually the opposite.
00:32
Top 25 % actually means there's 7%.
00:37
75th percentile.
00:41
Therefore, we have the probability that x is less than the 0 .75, or in this case, it less than a z.
01:05
Okay.
01:11
And with that, that would give the probability is 0 .75.
01:16
And we can use this to find our z score and plug it back into this equation.
01:23
This is a z score equation where the value minus the mean divided by the standard deviation.
01:30
Okay...