Suppose you are an investor with a choice between three securities that are identical in every way except in terms of their rates of return and risk.

Investment A:

Total return = 10 percent with probability 50 percent

Total return = 20 percent with probability 50 percent

Investment B:

Total return = 12 percent with probability 40 percent

Total return = 18 percent with probability 60 percent

Investment C:

Total return = 5 percent with probability 60 percent

Total return = 25 percent with probability 40 percent

The standard deviation of investment A is ____ percent.