00:05
All right, so we're told that the annual mean rates of return is standard deviation for financial assets of 10 % and 9%.
00:16
And then we're going to take 100 financial assets, and we're going to know the probability that of those 100 financial assets, that the return is less than 7%.
00:30
Now, we're only given that the mean and what the mean in standard deviation are of the population.
00:36
Because we have a large sample size n, due to the central limit theorem, which says that as long as n is greater than or equal to 30, then the distribution about the sample mean will be approximately normal.
00:49
So therefore, we can use a z score for this.
00:52
We can convert this 7 to a z score with this formula.
00:58
Z sub x bar is equal to the mean, minus the mean of the sampling distribution, which is the mean of the population.
01:06
So that's the same.
01:07
Divided by the standard error.
01:09
So the standard error, the way we calculate that is we take the population standard deviation divided by the square root of n.
01:15
So we get the mean that we're looking for is 7.
01:19
The mean of the distribution is 10.
01:22
Sigma is 9, and then root 100 here.
01:27
Great.
01:27
And then we're going to get our z score.
01:30
And right down here.
01:36
And this is what we get.
01:37
So we get the z score of negative 3 .3 repeating, which is negative 3 and 3.
01:42
And then that corresponds with the probability of 0 .00429, which as a percent would become, you know, move two decimal places over, so 0 .043%.
01:56
All right.
01:58
Then the second problem asks us about what are the assumptions of a random sample? well, first off, they have to be independent.
02:09
There's that.
02:15
And then, and that what i mean by that is that the probability of one person being selected has no impact on another person or thing being selected.
02:24
And then they also have to be mutually exclusive.
02:31
So if you're mutually exclusive, let me write that word out.
02:48
And what that means is if you're having two groups, one person or one thing can't be in both.
02:55
So you do need so you do mutually exclusive here.
02:59
And then the other piece that we need is that they have to come from the same probability distribution.
03:07
Because let's say you're sampling, let's just make something up.
03:11
Well, here we go.
03:12
Let's use our financial assets.
03:13
You're sampling the mean rates of return of financial assets and you select the hourly wage of an employee.
03:24
That's not the same probability distribution.
03:26
It doesn't, it's not there.
03:28
So they have to be in the same distribution.
03:33
And they don't have to be, you don't have to know anything about the distribution itself.
03:37
That's kind of what you're usually testing for.
03:39
I mean, sometimes you know, like we're, but we don't always.
03:43
All right.
03:44
The next part, three asks us about the default rate.
03:51
The default rate is about 8%, 8%, which is 0 .08.
03:57
And then there are 100 ,000 student loans made at this government institution.
04:05
So there's 8 % default rate on government guaranteed student loans...