Question 668663
mean = E[X] = x*P(x) for each x = 1*.1 + 2*.8 + 3* .1 = .1 + 1.6 + .3 = {{{highlight(2)}}}

Calculate E[X^2] in order to find Variance.  E[X^2] = 1^2 * .1 + 2^2 *.8 + 3^2 * .1 = .1 + 3.2 + .9 = 4.2

Var[X] = E[X^2] - E[X]^2 = 4.2 - 2^2 = 4.2 - 4 = .2

SD[X] = sqrt(Var[X]) = sqrt(.2) = {{{highlight(.4472)}}}