Miles per gallon. In its Fuel Economy Guide for 2008 model vehicles, the Environmental Protection Agency gives data on 1152 vehicles.
There are a number of outliers, mainly vehicles with very poor gas mileage.
If we ignore the outliers, however, the combined city and highway gas mileage of the other 1120 or so vehicles is approximately Normal with mean 18.7 miles per gallon (mpg) and standard deviation 4.3 mpg.
The quartiles of any distribution are the values with cumulative proportions 0.25 and 0.75.
They span the middle half of the distribution.
What are the quartiles of the distribution of gas mileage?
What is the first quartile of the distribution of gas mileage?