Question 417679
mean = {{{mu = 1*0.1 + 2*0.2 + 3*0.7 = 2.6}}}

variance = {{{sigma^2 = E(X^2) - (E(X))^2 = 1^2*0.1 + 2^2*0.2 + 3^2*0.7 - 2.6^2

= 7.2 - 6.76 = 0.44 }}}
==> standard deviation = {{{sigma = sqrt(0.44) = 0.6633}}}, to 4 decimal places.