Suppose authorities in Chicago, Illinois, would like to estimate the mean number of days to complete graffiti removal request from private property owners. Weekly mean number of days to complete requests from 2011 to 2012 are available in the file “Chicago Performance: Metrics_-_Streets___Sanitation_-_Graffiti_Removal.” Authorities determined the data is representative of the current environment in the city.
a) Construct a 99% confidence interval for the mean number of days to complete graffiti removal these days.
b) Construct a histogram of the weekly mean number of days to complete requests. Is it approximately normal?