# How do I find the standard deviation of a portfolio? [closed]

Compute the expected return $\mu_V$ and standard deviation $\sigma_V$ of a portfolio consisting of three securities with weights $\omega_1=40\%$, $\omega_2=-20\%$, $\omega_3=80\%$, given that the securities have expected reuturns $\mu_1=8\%$, $\mu_2=10\%$, $\mu_3=6\%$, standard deviations $\sigma_1=0.15$, $\sigma_2=0.05$, $\sigma_3=0.12$, and correlations $\rho_{12}=0.3$, $\rho_{23}=0$, $\rho_{31}=-0.2$.

I know how to compute the expected return of the portfolio, I got $\mu_V=0.06$, but I don't know how to calculate the standard deviation of a portfolio? What is the formula I need to use given the information? Do I need to find the variances given the standard deviations?

## closed as off-topic by Bob Jansen♦Feb 22 '16 at 6:27

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Basic financial questions are off-topic as they are assumed to be common knowledge for those studying or working in the field of quantitative finance." – Bob Jansen
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• @BobJansen So this is basic? – BCLC Feb 23 '16 at 18:39