The proportion is approximatly normally distributed..
The sample proportion is
So the 95% CI is given by
I'm stuck on this problem, i can't figure what the standard deviation is, and im not sure if 45 is the mean.
1) A new public telephone has been installed at the airport baggage-claim area. A quarter was lost 45 of the 300 times that it was used. Find a 95% confidence interval for the true proportion of times that a user will lose a quarter.