Given the following data for three possibile investments, A, B and C, calculate the coefficient of variation and with the aid of a diagram explain which is the least risky investment.

Expected Profit: A - 100 B - 120 C - 140
Standard Devi.: A - 10 B - 30 C - 20

I presume to calculate the COV you divide the standard deviation by the mean, to give you:

A: 100/10 = 0.1 B: 30/120 = 0.25 C: 20/140 = 0.14

I am struggling with how/what sort of diagram to use and how to explain which is the least risky investment. Any ideas would be great.