Question 359003
Mean = {{{mu = 1*0.1 + 2*0.2 + 3*0.7 = 2.6}}}
Variance = {{{sigma^2 = (1-2.6)^2*0.1  + (2-2.6)^2*0.2 + (7-2.6)^2*0.7}}}
={{{2.56*0.1+0.36*0.2+19.36*0.7 = 13.88}}}.
Thus ,
standard deviation = {{{sigma = sqrt(13.88) = 3.7256}}}, to four decimal places.