Question 463368
The experiment follows a binomial experiment with n = 90, p = 1/5, and q = 4/5.

==> {{{mu = np = 90*(1/5) = 18}}}, and 

{{{sigma^2 = npq = 90*(1/5)*(4/5) = 72/5}}} 

==> {{{sigma = sqrt(72/5) = (6sqrt(10))/5}}}