Question 984258
{{{p=180/400=0.45}}}
{{{SE=sqrt((p(1-p))/N)=sqrt((0.45)(0.55))/400)=0.02487}}}
{{{1.645*.02487=0.041}}}
So the 90% confidence interval would be,
{{{0.409<p<0.491}}}
This is nowhere near the 60% the electric company estimates so evidence exists to reject the claim.