You are trying to calculate the standard deviation of your portfolio that contains asset A, B and C. Consider the following:
Asset A: The current price of stock A is $10 per share. There is a 50% chance that at the end of the year (i.e., 1 year from today), the share price will be $11, and there is a 50% chance that at the end of the year, the share price will be $12. The probability that the stock will pay any dividend is zero.
Asset B: The standard deviation of stock B is 14%.
Asset C: The variance of asset C is zero.
The correlation between asset A and B is 0.7, while the correlation between asset B and C is zero, and the correlation between asset A and C is also zero. Your total investment in the portfolio is $400,000, out of which $200,000 has been invested in asset C. The remainder of the investment is equally distributed between asset A and B. What is the standard deviation of your portfolio?