(d) The following plots display the sample distribution of paired differences (weight| method Groove method). Do the plots provide any clear indication against the assumption of a normally distributed population? Explain. (2 marks) Histogram of diff Normal Q-Q Plot Frequency 2 -20 2 4 6 8 diff 8 9 Sample Quantiles 4 Z 60 -1.5 -0.5 0.5 1.5 Theoretical Quantiles 6 3. R. Sitchler et al. compared two methods of measuring treadwear in their paper "Measurement of Treadwear of Commercial Tires" (Rubber Age, Vol. 73:2). Eleven randomly chosen tires were each measured for treadwear by two methods, one based on weight and the other on groove wear. The data, in thousands of miles, are as follows. Groove Weight Groove Weight method method method method 30.5 28.7 24.5 16.1 30.9 25.9 20.9 19.9 31.9 23.3 18.9 15.2 30.4 23.1 13.7 11.5 27.3 23.7 11.4 11.2 20.4 20.9