Question 1182740
The 99% confidence interval will be 

{{{p[1] +- t[0.995]*sqrt((p[1]*(1-p[1]))/n)

= 276/345 +- (2.59)*sqrt((0.8*0.2)/345)

= 0.8 +- (2.59)*sqrt((0.8*0.2)/345) }}}

 0.744224 < p < 0.855776