00:01
We're looking at a normal distribution here.
00:03
So let's start by drawing it.
00:09
The mean, mu, is 15, and the standard deviation is 4.
00:14
And we're using the 68, 95, 99 .7 rule here.
00:20
68 95 99 .7.
00:24
And it's all about what percentage of the area of this curve, i .e., what percentage of values in the distribution, are in certain segments of it.
00:36
I put some lines down here.
00:43
Say, okay, so this is the mean, zero standard deviations away from the mean.
00:48
This is one above the mean, two above the mean, and three standard deviations.
00:53
This is minus one, minus two, and minus three.
00:56
So the rule is approximately 68 % is between minus one and one, 95 % between minus two and two, and 99 .7 % between minus three and three.
01:10
So here we want between 15 and 23.
01:15
So what is 23? well, 23 is the mean plus two standard deviations...