A fuel-economy study was conducted for two German automobiles, Mercedes and Volkswagen. One vehicle of each brand was selected, and the mileage performance was observed for 10 tanks of fuel in each car. The data are as follows (in miles per gallon):

(a) Construct a normal probability plot of each of the data sets. Based on these plots, is it reasonable to assume that they are each drawn from a normal population?
(b) Suppose that it was determined that the lowest observation of the Mercedes data was erroneously recorded and should be 24.6. Furthermore, the lowest observation of the Volkswagen data was also mistaken and should be 39.6. Again construct normal probability plots of each of the data sets with the corrected values. Based on these new plots, is it reasonable to assume that they are each drawn from a normal population?
(c) Compare your answers from parts (a) and (b) and comment on the effect of these mistaken observations on the normality assumption.
(d) Using the corrected data from part (b) and a 95% confidence interval, is there evidence to support the claim that the variability in mileage performance is greater for a Volkswagen than for a Mercedes?

Transcribed Image Text:

Volkswagen Mercedes 42.8 24.7 24.9 41.7 24.8 24.6 42.3 42.4 24.9 23.9 41.6 39.9 24.7 24.9 39.5 40.8 41.9 24.5 24.8 29.6