Question 1197914
{{{ME = z*sigma/sqrt(n)}}} 
0r
{{{n = (z*sigma/ME)^2}}} 
81.26% confidence interval  {{{(100-81.26)/2}}}= 9.7%  z(.8126 + .097) = 1.34 
 
 {{{n =(30*1.34/9)^2}}} = 19.98  (always round Up )
n = 20