00:01
So we're looking at a normal distribution.
00:03
Its mean mu is 20 .9, its standard deviation sigma is 39 .3.
00:10
So i'll draw a normal distribution to go along with this.
00:15
So first of all we pick an observation.
00:18
What's the probability it is less than 12? so 12 is below the mean.
00:23
We want less than, so the area to the left.
00:27
So normal distribution is...
00:30
There are functions that take you from values of the curve to the area under the curve but they're really complicated.
00:37
We don't do this by hand.
00:38
So you need something with the normal distribution built into it.
00:42
And here i would recommend technology.
00:44
If you use z -score tables it will make you round your z -scores and you will lose accuracy.
00:49
So you could use software like excel or r or matlab or you could use a calculator.
00:56
I'm going to use a ti -84 with the normal cdf function.
01:02
Into this i need to put a lower bound and upper bound.
01:06
Let's put them up here.
01:07
Lower bound, upper bound, mean, standard deviation.
01:10
And it will give me the area between the lower and upper bounds.
01:14
So for part a, well the lower bound should really be minus infinity.
01:20
The normal distribution goes on forever...