Question 1186554
The lower z-value is computed as follows:  {{{z = ("p'"-p)/( sqrt((p*(1-p))/n) ) = (0.78-0.80)/  sqrt((0.8*0.2)/81  ) = red(-0.45)}}}.

The upper z-value is computed as follows:  {{{z = ("p'"-p)/( sqrt((p*(1-p))/n) ) = (0.85-0.80)/  sqrt((0.8*0.2)/81  ) = red(1.125)}}}.


Thus, {{{P(.78 < "p'" < 0.85) = P(-0.45 <z < 1.125) = 0.870-0.326 = red(0.544)}}}