*if the stocks are perfectly positively correlated*. If this is the case, you can save yourself a heap of time by avoiding the long calculation: σ portfolio = [W

_{1}

^{2}σ

_{1}

^{2}+ W

_{2}

^{2}σ

_{2}

^{2}+ 2W

_{1}W

_{2}σ

_{1}σ

_{2}r

_{1,2}]

^{1/2}

If the two stocks, or whatever type of assets, have a correlation of 1.0, then you can simply find a weighted average.

Here's an example: If 30% of an investor's portfolio consists of an asset with a standard deviation of 0.4 and 70% consists of an asset with a standard deviation of 0.2, you can solve for the overall standard deviation of the portfolio like this:

(0.3)(0.4) + (0.7)(0.2) = 0.12 + 0.14 =

__0.26__

Now isn't that a lot faster than dragging out the long calculation with all those 0's and chances to miss a button. Lets hope there's a question like this on December 7th!