I was trying to solve the following exercise:
"Stocks A have $\mu_A=8\%$, $\sigma_A=2,5\%$ and stocks B have $\mu_B=6\%$, $\sigma_B=1,2\%$. Let us suppose that expexted returns are independent. What is the standard deviation of a portfolio made up of one stock A and one stock B?"
Since expected returns are independent, I immediately thought of the formula $$\sigma_P^2=w\sigma_A^2+(1-w)\sigma_B^2,$$ where $w$ represents the weight of stock A in the portfolio.
So I was wondering whether in the text there is a missing value, such as the weight of one stock in the portfolio. I don't think I can assume stocks are equally weighted. Anyway the final result is $2.77\%$. Thanks in advance.