00:01
We're looking at bone density, which is normally distributed, and we need to identify the correct graph.
00:08
So we have our normal distribution.
00:11
We want the probability that a score is less than 1 .95.
00:16
So with a mean of zero and a standard deviation of 1, this isn't just a normal distribution.
00:22
This is the standard normal distribution, where the scores and the z scores turn out to be the same.
00:28
Because the z score, z is just your data point minus the mean over standard deviation.
00:35
So here, z and x are the same.
00:39
So 1 .95 is 1 .95 standard deviations above the mean.
00:45
So it's going to be up here somewhere.
00:48
And we want any score less than that.
00:51
So that would be anything to the left.
00:54
So the answer here is c.
00:56
Looks like a is between minus 1 .95 and 1 .95.
01:02
B is greater than 1 .95.
01:04
D is less than minus 1 .5.
01:08
Now, how's we actually find this probability? we already have the z score...