Ex$.4$ Calculating average return and standard deviation for a portfolio given historical data.

You have the following information for three stocks for $2015-2019.$

Rate of Return $(\%)$

$\backslash$table$[[$Year$,$Stock M$,$Stock A$,$Stock B$,$Portfolio,$],[2015,15,25,10,17\mathrm{.}5,0\mathrm{.}5(25)+0\mathrm{.}5(10)**$