Problem 26.4

sigma=.;
h=1/12;

stockprices = {80, 64, 80,64,80,100,80,64,80};
Num=Length[stockprices];

ListPlot[stockprices, Joined->True, PlotStyle->{PointSize[Medium],Blue},AxesLabel->{"Week","Price"},PlotLabel->"Stock Prices"]

stockreturns=Table[N[Log[stockprices[[i]]/stockprices[[i-1]]]],{i,2,Num}]
stockreturnavg = Mean[stockreturns]

StDev = Sqrt[Sum[(stockreturns[[i]]-stockreturnavg)^2,{i,1,Num-1}]/(Num-2)]

sigma=StDev/Sqrt[h]