Return to risk ratio probability question

Hello All,

I hope i've posted this in the right area as it seems to be a probability / stats question based on optimisation.

Whilst i don't have a full question (this is something i curious about) it would be a great help if you could provide me with a walk through for the basic example bellow. this way i can always extrapolate it to a larger set of numbers.

How would i go about calculating the following:

If i had two companies and their monthly share prices over several years and i wanted to find out which one of three ratios between the two companies was the best, how would i calculate the return to risk ration on it?

For example:

A B

12% 17%

15% 10%

19% 6%

15% 15%

And i wanted to make it 80% A and 20% B (or any other set of percentages)

What is the best way to calculate the return to risk ration using this break down?

Thanks for all the help