00:01
So we have a fund manager who is managing a portfolio.
00:06
That consists of 10 shares of stock a, 10 shares of stock a and eight shares of stock b.
00:13
And the price of a is a mean of 10 and a variance of 16.
00:18
And stock b is a mean of 12 and a variance of nine.
00:22
And the correlation between those prices is 0 .3.
00:26
So we're going to find the mean and variance of the portfolio.
00:29
So let's first find the total.
00:32
The portfolio.
00:34
Well, that's going to be the number of shares times the mean.
00:37
So, because generally need to get a value.
00:39
So if the means 10, we have 10 of them.
00:42
It's going to be 100 plus 8 times 12, which is 96.
00:48
So the total value of our portfolio is $196, we'll say.
00:57
And then let's see, we need to find the weights.
01:03
So the weight of each stock is going to be by the total value of the stock divided by the value of the portfolio.
01:09
So the weight will be for the for a will be 100 over 186 and then to figure out this value would just do one minus 100 one 86 or you could do 96 over 196.
01:25
So the same thing with that.
01:27
Those are weights so because the mean of the portfolio is given as the the weight of a plus or time excuse me the the the mean of the of a and we're going to add to it the weight of b times the mean of b and we get the we do the appropriate multiplications and we get this 10 .979 and the variance is equal to the weight of a times the standard deviation or the square well sorry it's variance you should say of a we're told the variance so the weight is just you literally square the weight right here, take that number and you square it.
02:18
So it would be 0 .51 squared times 16 in this case.
02:24
And then we add to it the weight of b squared times the variance of b squared.
02:29
And then we're going to add to this two times the correlation r between a and b times the standard deviation of a times the standard deviation of b.
02:40
And the way you get the standard deviation is you take the square root of the variance...